diff --git a/clients/graphql-kotlin-client-jackson/build.gradle.kts b/clients/graphql-kotlin-client-jackson/build.gradle.kts
index 96ddeff4a1..985c457fd8 100644
--- a/clients/graphql-kotlin-client-jackson/build.gradle.kts
+++ b/clients/graphql-kotlin-client-jackson/build.gradle.kts
@@ -14,7 +14,7 @@ tasks {
                 limit {
                     counter = "INSTRUCTION"
                     value = "COVEREDRATIO"
-                    minimum = "0.85".toBigDecimal()
+                    minimum = "0.89".toBigDecimal()
                 }
             }
         }
diff --git a/clients/graphql-kotlin-client-jackson/src/main/kotlin/com/expediagroup/graphql/client/jackson/GraphQLClientJacksonSerializer.kt b/clients/graphql-kotlin-client-jackson/src/main/kotlin/com/expediagroup/graphql/client/jackson/GraphQLClientJacksonSerializer.kt
index b835e1e95f..112d6b8b75 100644
--- a/clients/graphql-kotlin-client-jackson/src/main/kotlin/com/expediagroup/graphql/client/jackson/GraphQLClientJacksonSerializer.kt
+++ b/clients/graphql-kotlin-client-jackson/src/main/kotlin/com/expediagroup/graphql/client/jackson/GraphQLClientJacksonSerializer.kt
@@ -19,6 +19,7 @@ package com.expediagroup.graphql.client.jackson
 import com.expediagroup.graphql.client.jackson.types.JacksonGraphQLResponse
 import com.expediagroup.graphql.client.serializer.GraphQLClientSerializer
 import com.expediagroup.graphql.client.types.GraphQLClientRequest
+import com.fasterxml.jackson.annotation.JsonInclude
 import com.fasterxml.jackson.databind.DeserializationFeature
 import com.fasterxml.jackson.databind.JavaType
 import com.fasterxml.jackson.databind.ObjectMapper
@@ -34,6 +35,7 @@ class GraphQLClientJacksonSerializer(private val mapper: ObjectMapper = jacksonO
 
     init {
         mapper.enable(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE)
+        mapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY)
     }
 
     override fun serialize(request: GraphQLClientRequest<*>): String = mapper.writeValueAsString(request)
diff --git a/clients/graphql-kotlin-client-jackson/src/main/kotlin/com/expediagroup/graphql/client/jackson/serializers/OptionalInputSerializer.kt b/clients/graphql-kotlin-client-jackson/src/main/kotlin/com/expediagroup/graphql/client/jackson/serializers/OptionalInputSerializer.kt
new file mode 100644
index 0000000000..8c410c82fe
--- /dev/null
+++ b/clients/graphql-kotlin-client-jackson/src/main/kotlin/com/expediagroup/graphql/client/jackson/serializers/OptionalInputSerializer.kt
@@ -0,0 +1,42 @@
+/*
+ * Copyright 2021 Expedia, Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.expediagroup.graphql.client.jackson.serializers
+
+import com.expediagroup.graphql.client.jackson.types.OptionalInput
+import com.fasterxml.jackson.core.JsonGenerator
+import com.fasterxml.jackson.databind.JsonSerializer
+import com.fasterxml.jackson.databind.SerializerProvider
+
+class OptionalInputSerializer : JsonSerializer<OptionalInput<*>>() {
+
+    override fun isEmpty(provider: SerializerProvider, value: OptionalInput<*>?): Boolean {
+        return value == OptionalInput.Undefined
+    }
+
+    override fun serialize(value: OptionalInput<*>, gen: JsonGenerator, serializers: SerializerProvider) {
+        when (value) {
+            is OptionalInput.Undefined -> return
+            is OptionalInput.Defined -> {
+                if (value.value == null) {
+                    serializers.defaultNullValueSerializer.serialize(value.value, gen, serializers)
+                } else {
+                    serializers.findValueSerializer(value.value::class.java).serialize(value.value, gen, serializers)
+                }
+            }
+        }
+    }
+}
diff --git a/clients/graphql-kotlin-client-jackson/src/main/kotlin/com/expediagroup/graphql/client/jackson/types/OptionalInput.kt b/clients/graphql-kotlin-client-jackson/src/main/kotlin/com/expediagroup/graphql/client/jackson/types/OptionalInput.kt
new file mode 100644
index 0000000000..d93219fc8f
--- /dev/null
+++ b/clients/graphql-kotlin-client-jackson/src/main/kotlin/com/expediagroup/graphql/client/jackson/types/OptionalInput.kt
@@ -0,0 +1,41 @@
+/*
+ * Copyright 2021 Expedia, Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.expediagroup.graphql.client.jackson.types
+
+import com.expediagroup.graphql.client.jackson.serializers.OptionalInputSerializer
+import com.fasterxml.jackson.annotation.JsonCreator
+import com.fasterxml.jackson.annotation.JsonValue
+import com.fasterxml.jackson.databind.annotation.JsonSerialize
+
+@JsonSerialize(using = OptionalInputSerializer::class)
+sealed class OptionalInput<out T> {
+    /**
+     * Represents missing/undefined value.
+     */
+    @JsonSerialize(using = OptionalInputSerializer::class)
+    object Undefined : OptionalInput<Nothing>() {
+        override fun toString() = "Undefined"
+    }
+
+    /**
+     * Wrapper holding explicitly specified value including NULL.
+     */
+    @JsonSerialize(using = OptionalInputSerializer::class)
+    class Defined<out U> @JsonCreator constructor(@JsonValue val value: U?) : OptionalInput<U>() {
+        override fun toString(): String = "Defined(value=$value)"
+    }
+}
diff --git a/clients/graphql-kotlin-client-jackson/src/test/kotlin/com/expediagroup/graphql/client/jackson/GraphQLClientJacksonSerializerTest.kt b/clients/graphql-kotlin-client-jackson/src/test/kotlin/com/expediagroup/graphql/client/jackson/GraphQLClientJacksonSerializerTest.kt
index ef3d35b39e..74c4275b40 100644
--- a/clients/graphql-kotlin-client-jackson/src/test/kotlin/com/expediagroup/graphql/client/jackson/GraphQLClientJacksonSerializerTest.kt
+++ b/clients/graphql-kotlin-client-jackson/src/test/kotlin/com/expediagroup/graphql/client/jackson/GraphQLClientJacksonSerializerTest.kt
@@ -18,6 +18,7 @@ package com.expediagroup.graphql.client.jackson
 
 import com.expediagroup.graphql.client.jackson.data.EnumQuery
 import com.expediagroup.graphql.client.jackson.data.FirstQuery
+import com.expediagroup.graphql.client.jackson.data.InputQuery
 import com.expediagroup.graphql.client.jackson.data.OtherQuery
 import com.expediagroup.graphql.client.jackson.data.PolymorphicQuery
 import com.expediagroup.graphql.client.jackson.data.ScalarQuery
@@ -26,6 +27,7 @@ import com.expediagroup.graphql.client.jackson.data.polymorphicquery.SecondInter
 import com.expediagroup.graphql.client.jackson.types.JacksonGraphQLError
 import com.expediagroup.graphql.client.jackson.types.JacksonGraphQLResponse
 import com.expediagroup.graphql.client.jackson.types.JacksonGraphQLSourceLocation
+import com.expediagroup.graphql.client.jackson.types.OptionalInput
 import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
 import org.junit.jupiter.api.Test
 import java.util.UUID
@@ -61,8 +63,7 @@ class GraphQLClientJacksonSerializerTest {
             |  "variables": { "input": 1.0 }
             |},{
             |  "query": "OTHER_QUERY",
-            |  "operationName": "OtherQuery",
-            |  "variables": null
+            |  "operationName": "OtherQuery"
             |}]
         """.trimMargin()
 
@@ -236,4 +237,29 @@ class GraphQLClientJacksonSerializerTest {
         val deserialized = serializer.deserialize(rawResponse, EnumQuery(EnumQuery.Variables()).responseType())
         assertEquals(TestEnum.THREE, deserialized.data?.enumResult)
     }
+
+    @Test
+    fun `verify we can serialize optional inputs`() {
+        val query = InputQuery(
+            variables = InputQuery.Variables(
+                requiredInput = 123,
+                optionalIntInput = OptionalInput.Defined(123),
+                optionalStringInput = OptionalInput.Defined(null)
+            )
+        )
+        val rawQuery =
+            """{
+            |  "query": "INPUT_QUERY",
+            |  "operationName": "InputQuery",
+            |  "variables": {
+            |    "requiredInput": 123,
+            |    "optionalIntInput": 123,
+            |    "optionalStringInput": null
+            |  }
+            |}
+        """.trimMargin()
+
+        val serialized = serializer.serialize(query)
+        assertEquals(testMapper.readTree(rawQuery), testMapper.readTree(serialized))
+    }
 }
diff --git a/clients/graphql-kotlin-client-jackson/src/test/kotlin/com/expediagroup/graphql/client/jackson/data/InputQuery.kt b/clients/graphql-kotlin-client-jackson/src/test/kotlin/com/expediagroup/graphql/client/jackson/data/InputQuery.kt
new file mode 100644
index 0000000000..060cf5891f
--- /dev/null
+++ b/clients/graphql-kotlin-client-jackson/src/test/kotlin/com/expediagroup/graphql/client/jackson/data/InputQuery.kt
@@ -0,0 +1,42 @@
+/*
+ * Copyright 2021 Expedia, Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.expediagroup.graphql.client.jackson.data
+
+import com.expediagroup.graphql.client.jackson.types.OptionalInput
+import com.expediagroup.graphql.client.types.GraphQLClientRequest
+import kotlin.reflect.KClass
+
+class InputQuery(
+    override val variables: Variables
+) : GraphQLClientRequest<InputQuery.Result> {
+    override val query: String = "INPUT_QUERY"
+
+    override val operationName: String = "InputQuery"
+
+    override fun responseType(): KClass<Result> = Result::class
+
+    data class Variables(
+        val requiredInput: Int,
+        val optionalIntInput: OptionalInput<Int> = OptionalInput.Undefined,
+        val optionalStringInput: OptionalInput<String> = OptionalInput.Undefined,
+        val optionalBooleanInput: OptionalInput<Boolean> = OptionalInput.Undefined
+    )
+
+    data class Result(
+        val stringResult: String
+    )
+}
diff --git a/clients/graphql-kotlin-client-jackson/src/test/kotlin/com/expediagroup/graphql/client/jackson/serializers/OptionalInputSerializerTest.kt b/clients/graphql-kotlin-client-jackson/src/test/kotlin/com/expediagroup/graphql/client/jackson/serializers/OptionalInputSerializerTest.kt
new file mode 100644
index 0000000000..d98ca9a88d
--- /dev/null
+++ b/clients/graphql-kotlin-client-jackson/src/test/kotlin/com/expediagroup/graphql/client/jackson/serializers/OptionalInputSerializerTest.kt
@@ -0,0 +1,73 @@
+/*
+ * Copyright 2021 Expedia, Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.expediagroup.graphql.client.jackson.serializers
+
+import com.expediagroup.graphql.client.jackson.types.OptionalInput
+import com.fasterxml.jackson.annotation.JsonInclude
+import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+class OptionalInputSerializerTest {
+
+    private val mapper = jacksonObjectMapper()
+    init {
+        mapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY)
+    }
+
+    @Test
+    fun `verify undefined value is serialized to empty JSON`() {
+        val undefined = InputWrapper()
+        assertEquals("{}", mapper.writeValueAsString(undefined))
+    }
+
+    @Test
+    fun `verify null value is serialized correctly`() {
+        val explicitNull = InputWrapper(
+            optionalInput = OptionalInput.Defined(null),
+            optionalInputObject = OptionalInput.Defined(null),
+            optionalInputList = OptionalInput.Defined(null)
+        )
+        assertEquals("""{"optionalInput":null,"optionalInputObject":null,"optionalInputList":null}""", mapper.writeValueAsString(explicitNull))
+    }
+
+    @Test
+    fun `verify defined values are serialized correctly`() {
+        val defined = InputWrapper(
+            optionalInput = OptionalInput.Defined(123),
+            optionalInputObject = OptionalInput.Defined(BasicInput(OptionalInput.Defined("foo"))),
+            optionalInputList = OptionalInput.Defined(listOf("a", "b", "c"))
+        )
+        assertEquals("""{"optionalInput":123,"optionalInputObject":{"name":"foo"},"optionalInputList":["a","b","c"]}""", mapper.writeValueAsString(defined))
+    }
+
+    @Test
+    fun `verify inner undefined values are serialized correctly`() {
+        val nestedUndefined = InputWrapper(optionalInputObject = OptionalInput.Defined(BasicInput(name = OptionalInput.Undefined)))
+        assertEquals("""{"optionalInputObject":{}}""", mapper.writeValueAsString(nestedUndefined))
+    }
+
+    data class InputWrapper(
+        val optionalInput: OptionalInput<Int> = OptionalInput.Undefined,
+        val optionalInputObject: OptionalInput<BasicInput> = OptionalInput.Undefined,
+        val optionalInputList: OptionalInput<List<String>> = OptionalInput.Undefined
+    )
+
+    data class BasicInput(
+        val name: OptionalInput<String> = OptionalInput.Undefined
+    )
+}
diff --git a/clients/graphql-kotlin-client-serialization/build.gradle.kts b/clients/graphql-kotlin-client-serialization/build.gradle.kts
index e206a099d2..c28ee1a518 100644
--- a/clients/graphql-kotlin-client-serialization/build.gradle.kts
+++ b/clients/graphql-kotlin-client-serialization/build.gradle.kts
@@ -20,7 +20,7 @@ tasks {
                 limit {
                     counter = "INSTRUCTION"
                     value = "COVEREDRATIO"
-                    minimum = "0.73".toBigDecimal()
+                    minimum = "0.77".toBigDecimal()
                 }
             }
         }
diff --git a/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/GraphQLClientKotlinxSerializer.kt b/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/GraphQLClientKotlinxSerializer.kt
index 3d9b1192cd..060877f76a 100644
--- a/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/GraphQLClientKotlinxSerializer.kt
+++ b/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/GraphQLClientKotlinxSerializer.kt
@@ -41,6 +41,7 @@ class GraphQLClientKotlinxSerializer(private val jsonBuilder: JsonBuilder.() ->
         apply(jsonBuilder)
         classDiscriminator = "__typename"
         coerceInputValues = true
+        // encodeDefaults = false // need this for optional
         encodeDefaults = true
     }
 
diff --git a/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/serializers/AnyKSerializer.kt b/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/serializers/AnyKSerializer.kt
index 297fa97c9c..6628986b02 100644
--- a/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/serializers/AnyKSerializer.kt
+++ b/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/serializers/AnyKSerializer.kt
@@ -16,6 +16,7 @@
 
 package com.expediagroup.graphql.client.serialization.serializers
 
+import com.expediagroup.graphql.client.serialization.types.OptionalInput
 import kotlinx.serialization.KSerializer
 import kotlinx.serialization.descriptors.SerialDescriptor
 import kotlinx.serialization.descriptors.buildClassSerialDescriptor
@@ -47,30 +48,37 @@ object AnyKSerializer : KSerializer<Any?> {
     override val descriptor: SerialDescriptor = buildClassSerialDescriptor("Any")
 
     override fun serialize(encoder: Encoder, value: Any?) {
-        val jsonEncoder = encoder as JsonEncoder
-        val jsonElement = serializeAny(value)
-        jsonEncoder.encodeJsonElement(jsonElement)
+        serializeAny(value)?.let {
+            val jsonEncoder = encoder as JsonEncoder
+            jsonEncoder.encodeJsonElement(it)
+        }
     }
 
-    private fun serializeAny(value: Any?): JsonElement = when (value) {
+    private fun serializeAny(value: Any?): JsonElement? = when (value) {
         null -> JsonNull
+        is OptionalInput.Undefined -> null
+        is OptionalInput.Defined<*> -> serializeAny(value.value)
         is Map<*, *> -> {
-            val mapContents = value.entries.associate { mapEntry ->
-                mapEntry.key.toString() to serializeAny(mapEntry.value)
-            }
+            val mapContents = value.mapNotNull { (key, value) ->
+                serializeAny(value)?.let {
+                    key.toString() to it
+                }
+            }.toMap()
             JsonObject(mapContents)
         }
         is List<*> -> {
-            val arrayContents = value.map { listEntry -> serializeAny(listEntry) }
+            val arrayContents = value.mapNotNull { listEntry -> serializeAny(listEntry) }
             JsonArray(arrayContents)
         }
         is Number -> JsonPrimitive(value)
         is Boolean -> JsonPrimitive(value)
         is String -> JsonPrimitive(value)
         else -> {
-            val contents = value::class.memberProperties.associate { property ->
-                property.name to serializeAny(property.getter.call(value))
-            }
+            val contents = value::class.memberProperties.mapNotNull { property ->
+                serializeAny(property.getter.call(value))?.let {
+                    property.name to it
+                }
+            }.toMap()
             JsonObject(contents)
         }
     }
diff --git a/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/serializers/OptionalInputSerializer.kt b/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/serializers/OptionalInputSerializer.kt
new file mode 100644
index 0000000000..311f12e91d
--- /dev/null
+++ b/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/serializers/OptionalInputSerializer.kt
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2021 Expedia, Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.expediagroup.graphql.client.serialization.serializers
+
+import com.expediagroup.graphql.client.serialization.types.OptionalInput
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.descriptors.buildClassSerialDescriptor
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+
+/**
+ * KSerializer that supports serialization of optional input. Delegates to `AnyKSerializer` serializer logic for serializing the contents.
+ */
+object OptionalInputSerializer : KSerializer<OptionalInput<Any>> {
+
+    override val descriptor: SerialDescriptor = buildClassSerialDescriptor("OptionalInput")
+
+    override fun serialize(encoder: Encoder, value: OptionalInput<Any>) {
+        when (value) {
+            is OptionalInput.Undefined -> { return }
+            is OptionalInput.Defined<*> -> {
+                AnyKSerializer.serialize(encoder, value.value)
+            }
+        }
+    }
+
+    // undefined is only supported during client serialization
+    override fun deserialize(decoder: Decoder): OptionalInput<Any> = OptionalInput.Defined(AnyKSerializer.deserialize(decoder))
+}
diff --git a/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/types/OptionalInput.kt b/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/types/OptionalInput.kt
new file mode 100644
index 0000000000..d0345bfb77
--- /dev/null
+++ b/clients/graphql-kotlin-client-serialization/src/main/kotlin/com/expediagroup/graphql/client/serialization/types/OptionalInput.kt
@@ -0,0 +1,39 @@
+/*
+ * Copyright 2021 Expedia, Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.expediagroup.graphql.client.serialization.types
+
+import com.expediagroup.graphql.client.serialization.serializers.OptionalInputSerializer
+import kotlinx.serialization.Serializable
+
+@Serializable(with = OptionalInputSerializer::class)
+sealed class OptionalInput<out T> {
+    /**
+     * Represents missing/undefined value.
+     */
+    @Serializable(with = OptionalInputSerializer::class)
+    object Undefined : OptionalInput<Nothing>() {
+        override fun toString() = "UNDEFINED"
+    }
+
+    /**
+     * Wrapper holding explicitly specified value including NULL.
+     */
+    @Serializable(with = OptionalInputSerializer::class)
+    data class Defined<out U>(val value: U?) : OptionalInput<U>() {
+        override fun toString(): String = "Defined(value=$value)"
+    }
+}
diff --git a/clients/graphql-kotlin-client-serialization/src/test/kotlin/com/expediagroup/graphql/client/serialization/GraphQLClientKotlinXSerializerTest.kt b/clients/graphql-kotlin-client-serialization/src/test/kotlin/com/expediagroup/graphql/client/serialization/GraphQLClientKotlinXSerializerTest.kt
index b9724e1666..241dae3745 100644
--- a/clients/graphql-kotlin-client-serialization/src/test/kotlin/com/expediagroup/graphql/client/serialization/GraphQLClientKotlinXSerializerTest.kt
+++ b/clients/graphql-kotlin-client-serialization/src/test/kotlin/com/expediagroup/graphql/client/serialization/GraphQLClientKotlinXSerializerTest.kt
@@ -18,6 +18,7 @@ package com.expediagroup.graphql.client.serialization
 
 import com.expediagroup.graphql.client.serialization.data.EnumQuery
 import com.expediagroup.graphql.client.serialization.data.FirstQuery
+import com.expediagroup.graphql.client.serialization.data.InputQuery
 import com.expediagroup.graphql.client.serialization.data.OtherQuery
 import com.expediagroup.graphql.client.serialization.data.PolymorphicQuery
 import com.expediagroup.graphql.client.serialization.data.ScalarQuery
@@ -26,10 +27,12 @@ import com.expediagroup.graphql.client.serialization.data.polymorphicquery.Secon
 import com.expediagroup.graphql.client.serialization.types.KotlinxGraphQLError
 import com.expediagroup.graphql.client.serialization.types.KotlinxGraphQLResponse
 import com.expediagroup.graphql.client.serialization.types.KotlinxGraphQLSourceLocation
+import com.expediagroup.graphql.client.serialization.types.OptionalInput
 import kotlinx.serialization.decodeFromString
 import kotlinx.serialization.json.Json
 import org.junit.jupiter.api.Test
 import java.util.UUID
+import kotlin.test.Ignore
 import kotlin.test.assertEquals
 
 class GraphQLClientKotlinXSerializerTest {
@@ -214,4 +217,30 @@ class GraphQLClientKotlinXSerializerTest {
         val deserialized = serializer.deserialize(rawResponse, EnumQuery(EnumQuery.Variables()).responseType())
         assertEquals(TestEnum.THREE, deserialized.data?.enumResult)
     }
+
+    @Test
+    @Ignore("disabled until https://github.com/Kotlin/kotlinx.serialization/issues/1091 is resolved")
+    fun `verify we can serialize optional inputs`() {
+        val query = InputQuery(
+            variables = InputQuery.Variables(
+                requiredInput = 123,
+                optionalIntInput = OptionalInput.Defined(123),
+                optionalStringInput = OptionalInput.Defined(null)
+            )
+        )
+        val rawQuery =
+            """{
+            |  "query": "INPUT_QUERY",
+            |  "operationName": "InputQuery",
+            |  "variables": {
+            |    "requiredInput": 123,
+            |    "optionalIntInput": 123,
+            |    "optionalStringInput": null
+            |  }
+            |}
+        """.trimMargin()
+
+        val serialized = serializer.serialize(query)
+        assertEquals(rawQuery, serialized)
+    }
 }
diff --git a/clients/graphql-kotlin-client-serialization/src/test/kotlin/com/expediagroup/graphql/client/serialization/data/InputQuery.kt b/clients/graphql-kotlin-client-serialization/src/test/kotlin/com/expediagroup/graphql/client/serialization/data/InputQuery.kt
new file mode 100644
index 0000000000..9c0a2faa10
--- /dev/null
+++ b/clients/graphql-kotlin-client-serialization/src/test/kotlin/com/expediagroup/graphql/client/serialization/data/InputQuery.kt
@@ -0,0 +1,46 @@
+/*
+ * Copyright 2021 Expedia, Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.expediagroup.graphql.client.serialization.data
+
+import com.expediagroup.graphql.client.serialization.types.OptionalInput
+import com.expediagroup.graphql.client.types.GraphQLClientRequest
+import kotlinx.serialization.Serializable
+import kotlin.reflect.KClass
+
+@Serializable
+class InputQuery(
+    override val variables: Variables
+) : GraphQLClientRequest<InputQuery.Result> {
+    override val query: String = "INPUT_QUERY"
+
+    override val operationName: String = "InputQuery"
+
+    override fun responseType(): KClass<Result> = Result::class
+
+    @Serializable
+    data class Variables(
+        val requiredInput: Int,
+        val optionalIntInput: OptionalInput<Int> = OptionalInput.Undefined,
+        val optionalStringInput: OptionalInput<String> = OptionalInput.Undefined,
+        val optionalBooleanInput: OptionalInput<Boolean> = OptionalInput.Undefined
+    )
+
+    @Serializable
+    data class Result(
+        val stringResult: String
+    )
+}
diff --git a/clients/graphql-kotlin-client-serialization/src/test/kotlin/com/expediagroup/graphql/client/serialization/types/serializers/OptionalInputSerializerTest.kt b/clients/graphql-kotlin-client-serialization/src/test/kotlin/com/expediagroup/graphql/client/serialization/types/serializers/OptionalInputSerializerTest.kt
new file mode 100644
index 0000000000..c102f569ab
--- /dev/null
+++ b/clients/graphql-kotlin-client-serialization/src/test/kotlin/com/expediagroup/graphql/client/serialization/types/serializers/OptionalInputSerializerTest.kt
@@ -0,0 +1,75 @@
+/*
+ * Copyright 2021 Expedia, Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.expediagroup.graphql.client.serialization.types.serializers
+
+import com.expediagroup.graphql.client.serialization.types.OptionalInput
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.encodeToString
+import kotlinx.serialization.json.Json
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+class OptionalInputSerializerTest {
+
+    private val json = Json {
+        encodeDefaults = false
+    }
+
+    @Test
+    fun `verify undefined value is serialized to empty JSON`() {
+        val undefined = InputWrapper()
+        assertEquals("{}", json.encodeToString(undefined))
+    }
+
+    @Test
+    fun `verify null value is serialized correctly`() {
+        val explicitNull = InputWrapper(
+            optionalInput = OptionalInput.Defined(null),
+            optionalInputObject = OptionalInput.Defined(null),
+            optionalInputList = OptionalInput.Defined(null)
+        )
+        assertEquals("""{"optionalInput":null,"optionalInputObject":null,"optionalInputList":null}""", json.encodeToString(explicitNull))
+    }
+
+    @Test
+    fun `verify defined values are serialized correctly`() {
+        val defined = InputWrapper(
+            optionalInput = OptionalInput.Defined(123),
+            optionalInputObject = OptionalInput.Defined(BasicInput(OptionalInput.Defined("foo"))),
+            optionalInputList = OptionalInput.Defined(listOf("a", "b", "c"))
+        )
+        assertEquals("""{"optionalInput":123,"optionalInputObject":{"name":"foo"},"optionalInputList":["a","b","c"]}""", json.encodeToString(defined))
+    }
+
+    @Test
+    fun `verify inner undefined values are serialized correctly`() {
+        val nestedUndefined = InputWrapper(optionalInputObject = OptionalInput.Defined(BasicInput(name = OptionalInput.Undefined)))
+        assertEquals("""{"optionalInputObject":{}}""", json.encodeToString(nestedUndefined))
+    }
+
+    @Serializable
+    data class InputWrapper(
+        val optionalInput: OptionalInput<Int> = OptionalInput.Undefined,
+        val optionalInputObject: OptionalInput<BasicInput> = OptionalInput.Undefined,
+        val optionalInputList: OptionalInput<List<String>> = OptionalInput.Undefined
+    )
+
+    @Serializable
+    data class BasicInput(
+        val name: OptionalInput<String> = OptionalInput.Undefined
+    )
+}
diff --git a/examples/client/maven-client/pom.xml b/examples/client/maven-client/pom.xml
index 1f5aee3920..6f6b955860 100755
--- a/examples/client/maven-client/pom.xml
+++ b/examples/client/maven-client/pom.xml
@@ -81,6 +81,7 @@
                                 </customScalar>
                             </customScalars>
                             <serializer>JACKSON</serializer>
+                            <useOptionalInputWrapper>true</useOptionalInputWrapper>
                         </configuration>
                     </execution>
                 </executions>
diff --git a/examples/client/maven-client/src/main/kotlin/com/expediagroup/graphql/examples/client/maven/Application.kt b/examples/client/maven-client/src/main/kotlin/com/expediagroup/graphql/examples/client/maven/Application.kt
index 4492d57a23..5eac135592 100644
--- a/examples/client/maven-client/src/main/kotlin/com/expediagroup/graphql/examples/client/maven/Application.kt
+++ b/examples/client/maven-client/src/main/kotlin/com/expediagroup/graphql/examples/client/maven/Application.kt
@@ -16,6 +16,7 @@
 
 package com.expediagroup.graphql.examples.client.maven
 
+import com.expediagroup.graphql.client.jackson.types.OptionalInput
 import com.expediagroup.graphql.client.spring.GraphQLWebClient
 import com.expediagroup.graphql.generated.AddObjectMutation
 import com.expediagroup.graphql.generated.ExampleQuery
@@ -49,8 +50,8 @@ fun main() {
     runBlocking {
         val results = client.execute(
             listOf(
-                HelloWorldQuery(variables = HelloWorldQuery.Variables(name = null)),
-                HelloWorldQuery(variables = HelloWorldQuery.Variables(name = "Dariusz"))
+                HelloWorldQuery(variables = HelloWorldQuery.Variables()),
+                HelloWorldQuery(variables = HelloWorldQuery.Variables(name = OptionalInput.Defined("Dariusz")))
             )
         )
 
@@ -75,7 +76,7 @@ fun main() {
 
     println("additional examples")
     runBlocking {
-        val exampleData = client.execute(ExampleQuery(variables = ExampleQuery.Variables(simpleCriteria = SimpleArgumentInput(max = 1.0f))))
+        val exampleData = client.execute(ExampleQuery(variables = ExampleQuery.Variables(simpleCriteria = OptionalInput.Defined(SimpleArgumentInput(max = OptionalInput.Defined(1.0f))))))
         println("\tretrieved interface: ${exampleData.data?.interfaceQuery} ")
         println("\tretrieved union: ${exampleData.data?.unionQuery} ")
         println("\tretrieved enum: ${exampleData.data?.enumQuery} ")
diff --git a/plugins/client/graphql-kotlin-client-generator/build.gradle.kts b/plugins/client/graphql-kotlin-client-generator/build.gradle.kts
index 59e4c4350b..e7d857e1b0 100644
--- a/plugins/client/graphql-kotlin-client-generator/build.gradle.kts
+++ b/plugins/client/graphql-kotlin-client-generator/build.gradle.kts
@@ -17,6 +17,7 @@ dependencies {
     api("org.jetbrains.kotlinx:kotlinx-serialization-json:$kotlinxSerializationVersion")
     implementation("io.ktor:ktor-client-cio:$ktorVersion")
     implementation("io.ktor:ktor-client-jackson:$ktorVersion")
+    testImplementation(project(path = ":graphql-kotlin-client-jackson"))
     testImplementation("com.github.tomakehurst:wiremock-jre8:$wireMockVersion")
     testImplementation("com.github.tschuchortdev:kotlin-compile-testing:$compileTestingVersion")
     testImplementation("org.junit.jupiter:junit-jupiter-params:$junitVersion")
diff --git a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generateClient.kt b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generateClient.kt
index f569f633ac..db844f975b 100644
--- a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generateClient.kt
+++ b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generateClient.kt
@@ -32,14 +32,16 @@ fun generateClient(
     customScalarsMap: List<GraphQLScalar> = emptyList(),
     serializer: GraphQLSerializer = GraphQLSerializer.JACKSON,
     schemaPath: String,
-    queries: List<File>
+    queries: List<File>,
+    useOptionalInputWrapper: Boolean = false
 ): List<FileSpec> {
     val customScalars = customScalarsMap.associateBy { it.scalar }
     val config = GraphQLClientGeneratorConfig(
         packageName = packageName,
         allowDeprecated = allowDeprecated,
         customScalarMap = customScalars,
-        serializer = serializer
+        serializer = serializer,
+        useOptionalInputWrapper = useOptionalInputWrapper
     )
     val generator = GraphQLClientGenerator(schemaPath, config)
     return generator.generate(queries)
diff --git a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGenerator.kt b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGenerator.kt
index e091ff5b7b..cb9d5b8571 100644
--- a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGenerator.kt
+++ b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGenerator.kt
@@ -104,7 +104,8 @@ class GraphQLClientGenerator(
                 queryDocument = queryDocument,
                 allowDeprecated = config.allowDeprecated,
                 customScalarMap = config.customScalarMap,
-                serializer = config.serializer
+                serializer = config.serializer,
+                useOptionalInputWrapper = config.useOptionalInputWrapper
             )
             val queryConstName = operationTypeName.toUpperUnderscore()
             val queryConstProp = PropertySpec.builder(queryConstName, STRING)
diff --git a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGeneratorConfig.kt b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGeneratorConfig.kt
index 699fc36708..f6b1dd79b2 100644
--- a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGeneratorConfig.kt
+++ b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGeneratorConfig.kt
@@ -27,7 +27,9 @@ data class GraphQLClientGeneratorConfig(
     /** Custom scalar type to converter mapping. */
     val customScalarMap: Map<String, GraphQLScalar> = emptyMap(),
     /** Type of JSON serializer to be used. */
-    val serializer: GraphQLSerializer = GraphQLSerializer.JACKSON
+    val serializer: GraphQLSerializer = GraphQLSerializer.JACKSON,
+    /** Explicit opt-in flag to enable support for optional inputs, only available for JACKSON serializer. */
+    val useOptionalInputWrapper: Boolean = false
 )
 
 /**
diff --git a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGeneratorContext.kt b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGeneratorContext.kt
index 8380c84112..ff40646e95 100644
--- a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGeneratorContext.kt
+++ b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/GraphQLClientGeneratorContext.kt
@@ -34,7 +34,8 @@ data class GraphQLClientGeneratorContext(
     val queryDocument: Document,
     val allowDeprecated: Boolean = false,
     val customScalarMap: Map<String, GraphQLScalar> = mapOf(),
-    val serializer: GraphQLSerializer = GraphQLSerializer.JACKSON
+    val serializer: GraphQLSerializer = GraphQLSerializer.JACKSON,
+    val useOptionalInputWrapper: Boolean = false
 ) {
     val typeSpecs: MutableMap<ClassName, TypeSpec> = mutableMapOf()
     val polymorphicTypes: MutableMap<ClassName, MutableList<ClassName>> = mutableMapOf()
@@ -49,3 +50,5 @@ data class GraphQLClientGeneratorContext(
     val classNameCache: MutableMap<String, MutableList<ClassName>> = mutableMapOf()
     val typeToSelectionSetMap: MutableMap<String, Set<String>> = mutableMapOf()
 }
+
+internal fun GraphQLClientGeneratorContext.isOptionalInputSupported() = useOptionalInputWrapper && serializer == GraphQLSerializer.JACKSON
diff --git a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/types/generateGraphQLInputObjectTypeSpec.kt b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/types/generateGraphQLInputObjectTypeSpec.kt
index 25341d0a15..2a0c6485e8 100644
--- a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/types/generateGraphQLInputObjectTypeSpec.kt
+++ b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/types/generateGraphQLInputObjectTypeSpec.kt
@@ -18,9 +18,13 @@ package com.expediagroup.graphql.plugin.client.generator.types
 
 import com.expediagroup.graphql.plugin.client.generator.GraphQLClientGeneratorContext
 import com.expediagroup.graphql.plugin.client.generator.GraphQLSerializer
+import com.expediagroup.graphql.plugin.client.generator.isOptionalInputSupported
+import com.squareup.kotlinpoet.ClassName
 import com.squareup.kotlinpoet.FunSpec
 import com.squareup.kotlinpoet.KModifier
+import com.squareup.kotlinpoet.MemberName
 import com.squareup.kotlinpoet.ParameterSpec
+import com.squareup.kotlinpoet.ParameterizedTypeName.Companion.parameterizedBy
 import com.squareup.kotlinpoet.PropertySpec
 import com.squareup.kotlinpoet.TypeSpec
 import graphql.language.InputObjectTypeDefinition
@@ -45,7 +49,14 @@ internal fun generateGraphQLInputObjectTypeSpec(context: GraphQLClientGeneratorC
         val kotlinFieldType = generateTypeName(context, fieldDefinition.type)
         val fieldName = fieldDefinition.name
 
-        val inputPropertySpecBuilder = PropertySpec.builder(fieldName, kotlinFieldType)
+        val inputFieldType = if (kotlinFieldType.isNullable && context.isOptionalInputSupported()) {
+            ClassName("com.expediagroup.graphql.client.jackson.types", "OptionalInput")
+                .parameterizedBy(kotlinFieldType.copy(nullable = false))
+        } else {
+            kotlinFieldType
+        }
+
+        val inputPropertySpecBuilder = PropertySpec.builder(fieldName, inputFieldType)
             .initializer(fieldName)
         fieldDefinition.description?.content?.let { kdoc ->
             inputPropertySpecBuilder.addKdoc("%L", kdoc)
@@ -55,8 +66,12 @@ internal fun generateGraphQLInputObjectTypeSpec(context: GraphQLClientGeneratorC
         inputObjectTypeSpecBuilder.addProperty(inputPropertySpec)
 
         val inputParameterSpec = ParameterSpec.builder(inputPropertySpec.name, inputPropertySpec.type)
-        if (inputPropertySpec.type.isNullable) {
-            inputParameterSpec.defaultValue("null")
+        if (kotlinFieldType.isNullable) {
+            if (context.isOptionalInputSupported()) {
+                inputParameterSpec.defaultValue("%M", MemberName("com.expediagroup.graphql.client.jackson.types", "OptionalInput.Undefined"))
+            } else {
+                inputParameterSpec.defaultValue("null")
+            }
         }
         constructorBuilder.addParameter(inputParameterSpec.build())
     }
diff --git a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/types/generateVariableTypeSpec.kt b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/types/generateVariableTypeSpec.kt
index 935f5e6ba7..3a48309c39 100644
--- a/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/types/generateVariableTypeSpec.kt
+++ b/plugins/client/graphql-kotlin-client-generator/src/main/kotlin/com/expediagroup/graphql/plugin/client/generator/types/generateVariableTypeSpec.kt
@@ -18,9 +18,13 @@ package com.expediagroup.graphql.plugin.client.generator.types
 
 import com.expediagroup.graphql.plugin.client.generator.GraphQLClientGeneratorContext
 import com.expediagroup.graphql.plugin.client.generator.GraphQLSerializer
+import com.expediagroup.graphql.plugin.client.generator.isOptionalInputSupported
+import com.squareup.kotlinpoet.ClassName
 import com.squareup.kotlinpoet.FunSpec
 import com.squareup.kotlinpoet.KModifier
+import com.squareup.kotlinpoet.MemberName
 import com.squareup.kotlinpoet.ParameterSpec
+import com.squareup.kotlinpoet.ParameterizedTypeName.Companion.parameterizedBy
 import com.squareup.kotlinpoet.PropertySpec
 import com.squareup.kotlinpoet.TypeSpec
 import graphql.language.VariableDefinition
@@ -39,14 +43,24 @@ internal fun generateVariableTypeSpec(context: GraphQLClientGeneratorContext, va
     val constructorSpec = FunSpec.constructorBuilder()
     variableDefinitions.forEach { variableDef ->
         val kotlinTypeName = generateTypeName(context, variableDef.type)
+        val variableTypeName = if (kotlinTypeName.isNullable && context.isOptionalInputSupported()) {
+            ClassName("com.expediagroup.graphql.client.jackson.types", "OptionalInput")
+                .parameterizedBy(kotlinTypeName.copy(nullable = false))
+        } else {
+            kotlinTypeName
+        }
 
-        val parameterBuilder = ParameterSpec.builder(variableDef.name, kotlinTypeName)
+        val parameterBuilder = ParameterSpec.builder(variableDef.name, variableTypeName)
         if (kotlinTypeName.isNullable) {
-            parameterBuilder.defaultValue("null")
+            if (context.isOptionalInputSupported()) {
+                parameterBuilder.defaultValue("%M", MemberName("com.expediagroup.graphql.client.jackson.types", "OptionalInput.Undefined"))
+            } else {
+                parameterBuilder.defaultValue("null")
+            }
         }
         constructorSpec.addParameter(parameterBuilder.build())
         variableTypeSpec.addProperty(
-            PropertySpec.builder(variableDef.name, kotlinTypeName)
+            PropertySpec.builder(variableDef.name, variableTypeName)
                 .initializer(variableDef.name)
                 .build()
         )
diff --git a/plugins/client/graphql-kotlin-client-generator/src/test/data/jackson/variables/JacksonInputQuery.kt b/plugins/client/graphql-kotlin-client-generator/src/test/data/jackson/variables/JacksonInputQuery.kt
index db293267d9..8d66f02cf8 100644
--- a/plugins/client/graphql-kotlin-client-generator/src/test/data/jackson/variables/JacksonInputQuery.kt
+++ b/plugins/client/graphql-kotlin-client-generator/src/test/data/jackson/variables/JacksonInputQuery.kt
@@ -1,5 +1,7 @@
 package com.expediagroup.graphql.generated
 
+import com.expediagroup.graphql.client.jackson.types.OptionalInput
+import com.expediagroup.graphql.client.jackson.types.OptionalInput.Undefined
 import com.expediagroup.graphql.client.types.GraphQLClientRequest
 import com.expediagroup.graphql.generated.inputs.SimpleArgumentInput
 import kotlin.Boolean
@@ -20,7 +22,7 @@ public class JacksonInputQuery(
       JacksonInputQuery.Result::class
 
   public data class Variables(
-    public val input: SimpleArgumentInput? = null
+    public val input: OptionalInput<SimpleArgumentInput> = OptionalInput.Undefined
   )
 
   public data class Result(
diff --git a/plugins/client/graphql-kotlin-client-generator/src/test/data/jackson/variables/inputs/SimpleArgumentInput.kt b/plugins/client/graphql-kotlin-client-generator/src/test/data/jackson/variables/inputs/SimpleArgumentInput.kt
index 092181ceb9..9205ed67e3 100644
--- a/plugins/client/graphql-kotlin-client-generator/src/test/data/jackson/variables/inputs/SimpleArgumentInput.kt
+++ b/plugins/client/graphql-kotlin-client-generator/src/test/data/jackson/variables/inputs/SimpleArgumentInput.kt
@@ -1,5 +1,7 @@
 package com.expediagroup.graphql.generated.inputs
 
+import com.expediagroup.graphql.client.jackson.types.OptionalInput
+import com.expediagroup.graphql.client.jackson.types.OptionalInput.Undefined
 import kotlin.Float
 import kotlin.String
 
@@ -10,13 +12,13 @@ public data class SimpleArgumentInput(
   /**
    * Maximum value for test criteria
    */
-  public val max: Float? = null,
+  public val max: OptionalInput<Float> = OptionalInput.Undefined,
   /**
    * Minimum value for test criteria
    */
-  public val min: Float? = null,
+  public val min: OptionalInput<Float> = OptionalInput.Undefined,
   /**
    * New value to be set
    */
-  public val newName: String? = null
+  public val newName: OptionalInput<String> = OptionalInput.Undefined
 )
diff --git a/plugins/client/graphql-kotlin-client-generator/src/test/kotlin/com/expediagroup/graphql/plugin/client/generator/GenerateJacksonClientIT.kt b/plugins/client/graphql-kotlin-client-generator/src/test/kotlin/com/expediagroup/graphql/plugin/client/generator/GenerateJacksonClientIT.kt
index 3cf6b0b97c..56ae20854b 100755
--- a/plugins/client/graphql-kotlin-client-generator/src/test/kotlin/com/expediagroup/graphql/plugin/client/generator/GenerateJacksonClientIT.kt
+++ b/plugins/client/graphql-kotlin-client-generator/src/test/kotlin/com/expediagroup/graphql/plugin/client/generator/GenerateJacksonClientIT.kt
@@ -28,7 +28,8 @@ class GenerateJacksonClientIT {
     fun `verify generation of client code using jackson`(testDirectory: File) {
         val config = defaultConfig.copy(
             serializer = GraphQLSerializer.JACKSON,
-            customScalarMap = mapOf("UUID" to GraphQLScalar("UUID", "java.util.UUID", "com.expediagroup.graphql.plugin.client.generator.UUIDScalarConverter"))
+            customScalarMap = mapOf("UUID" to GraphQLScalar("UUID", "java.util.UUID", "com.expediagroup.graphql.plugin.client.generator.UUIDScalarConverter")),
+            useOptionalInputWrapper = true
         )
         verifyClientGeneration(config, testDirectory)
     }
diff --git a/plugins/graphql-kotlin-gradle-plugin/README.md b/plugins/graphql-kotlin-gradle-plugin/README.md
index d80e57e97d..0e7ea9316d 100755
--- a/plugins/graphql-kotlin-gradle-plugin/README.md
+++ b/plugins/graphql-kotlin-gradle-plugin/README.md
@@ -53,6 +53,9 @@ graphql {
           // Read timeout in milliseconds
           read = 15_000
       }
+      // Opt-in flag to wrap nullable arguments in OptionalInput that distinguish between null and undefined value.
+      // Only supported for JACKSON serializer
+      useOptionalInputWrapper = false
   }
   schema {
       // List of supported packages that can contain GraphQL schema type definitions
@@ -103,6 +106,7 @@ resulting generated code will be automatically added to the project main source
 | `serializer` | GraphQLSerializer | | JSON serializer that will be used to generate the data classes.<br/>**Default value is:** `GraphQLSerializer.JACKSON`. |
 | `schemaFile` | File | `schemaFileName` or `schemaFile` has to be provided | GraphQL schema file that will be used to generate client code. |
 | `schemaFileName` | String | `schemaFileName` or `schemaFile` has to be provided | Path to GraphQL schema file that will be used to generate client code.<br/>**Command line property is**: `schemaFileName`. |
+| `useOptionalInputWrapper` | Boolean | | Boolean opt-in flag to wrap nullable arguments in `OptionalInput` that distinguish between `null` and undefined/omitted value. Only supported for JACKSON serializer.<br/>**Default value is:** `false`.<br/>**Command line property is**: `useOptionalInputWrapper` |
 
 ### graphqlGenerateSDL
 
@@ -150,6 +154,7 @@ test source set.
 | `serializer` | GraphQLSerializer | | JSON serializer that will be used to generate the data classes.<br/>**Default value is:** `GraphQLSerializer.JACKSON`. |
 | `schemaFile` | File | `schemaFileName` or `schemaFile` has to be provided | GraphQL schema file that will be used to generate client code. |
 | `schemaFileName` | String | `schemaFileName` or `schemaFile` has to be provided | Path to GraphQL schema file that will be used to generate client code.<br/>**Command line property is**: `schemaFileName`. |
+| `useOptionalInputWrapper` | Boolean | | Boolean opt-in flag to wrap nullable arguments in `OptionalInput` that distinguish between `null` and undefined/omitted value. Only supported for JACKSON serializer.<br/>**Default value is:** `false`.<br/>**Command line property is**: `useOptionalInputWrapper` |
 
 ### graphqlIntrospectSchema
 
diff --git a/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLGradlePlugin.kt b/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLGradlePlugin.kt
index f69a599b79..399f2b23f8 100644
--- a/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLGradlePlugin.kt
+++ b/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLGradlePlugin.kt
@@ -96,6 +96,7 @@ class GraphQLGradlePlugin : Plugin<Project> {
                 }
                 generateClientTask.queryFiles.setFrom(extension.clientExtension.queryFiles)
                 generateClientTask.serializer.convention(extension.clientExtension.serializer)
+                generateClientTask.useOptionalInputWrapper.convention(extension.clientExtension.useOptionalInputWrapper)
 
                 when {
                     extension.clientExtension.endpoint != null -> {
diff --git a/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLPluginExtension.kt b/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLPluginExtension.kt
index 247ea22a68..c5e7ec9ee7 100644
--- a/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLPluginExtension.kt
+++ b/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLPluginExtension.kt
@@ -73,6 +73,8 @@ open class GraphQLPluginClientExtension {
     var queryFileDirectory: String? = null
     /** JSON serializer that will be used to generate the data classes. */
     var serializer: GraphQLSerializer = GraphQLSerializer.JACKSON
+    /** Opt-in flag to wrap nullable arguments in OptionalInput that supports both null and undefined. Only supported for JACKSON serializer. */
+    var useOptionalInputWrapper: Boolean = false
 
     /** Connect and read timeout configuration for executing introspection query/download schema */
     internal val timeoutConfig: TimeoutConfiguration = TimeoutConfiguration()
diff --git a/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/actions/GenerateClientAction.kt b/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/actions/GenerateClientAction.kt
index 38a0857460..5dcc99f12b 100644
--- a/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/actions/GenerateClientAction.kt
+++ b/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/actions/GenerateClientAction.kt
@@ -38,8 +38,9 @@ abstract class GenerateClientAction : WorkAction<GenerateClientParameters> {
         val schemaPath = parameters.schemaPath.get()
         val queryFiles = parameters.queryFiles.get()
         val targetDirectory = parameters.targetDirectory.get()
+        val useOptionalInputWrapper = parameters.useOptionalInputWrapper.get()
 
-        generateClient(targetPackage, allowDeprecated, customScalarMap, serializer, schemaPath, queryFiles).forEach {
+        generateClient(targetPackage, allowDeprecated, customScalarMap, serializer, schemaPath, queryFiles, useOptionalInputWrapper).forEach {
             it.writeTo(targetDirectory)
         }
     }
diff --git a/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/parameters/GenerateClientParameters.kt b/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/parameters/GenerateClientParameters.kt
index 4f377eee11..acf2db08b1 100644
--- a/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/parameters/GenerateClientParameters.kt
+++ b/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/parameters/GenerateClientParameters.kt
@@ -42,4 +42,9 @@ interface GenerateClientParameters : WorkParameters {
     val queryFiles: ListProperty<File>
     /** Directory where to save the generated source files. */
     val targetDirectory: Property<File>
+    /**
+     * Explicit opt-in flag to wrap nullable arguments in OptionalInput that supports both null and undefined values.
+     * Only supported for JACKSON serializer.
+     */
+    val useOptionalInputWrapper: Property<Boolean>
 }
diff --git a/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/tasks/AbstractGenerateClientTask.kt b/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/tasks/AbstractGenerateClientTask.kt
index 08d0056d34..9a52880289 100755
--- a/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/tasks/AbstractGenerateClientTask.kt
+++ b/plugins/graphql-kotlin-gradle-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/gradle/tasks/AbstractGenerateClientTask.kt
@@ -124,6 +124,11 @@ abstract class AbstractGenerateClientTask : DefaultTask() {
     @Option(option = "serializer", description = "JSON serializer that will be used to generate the data classes.")
     val serializer: Property<GraphQLSerializer> = project.objects.property(GraphQLSerializer::class.java)
 
+    @Input
+    @Optional
+    @Option(option = "useOptionalInputWrapper", description = "Opt-in flag to wrap nullable arguments in OptionalInput that supports both null and undefined.")
+    val useOptionalInputWrapper: Property<Boolean> = project.objects.property(Boolean::class.java)
+
     @OutputDirectory
     val outputDirectory: DirectoryProperty = project.objects.directoryProperty()
 
@@ -139,6 +144,7 @@ abstract class AbstractGenerateClientTask : DefaultTask() {
         serializer.convention(GraphQLSerializer.JACKSON)
         queryFileDirectory.convention("${project.projectDir}/src/main/resources")
         outputDirectory.convention(project.layout.buildDirectory.dir("generated/source/graphql/main"))
+        useOptionalInputWrapper.convention(false)
     }
 
     @Suppress("EXPERIMENTAL_API_USAGE")
@@ -185,6 +191,7 @@ abstract class AbstractGenerateClientTask : DefaultTask() {
             parameters.schemaPath.set(graphQLSchemaPath)
             parameters.queryFiles.set(targetQueryFiles)
             parameters.targetDirectory.set(targetDirectory)
+            parameters.useOptionalInputWrapper.set(useOptionalInputWrapper)
         }
         workQueue.await()
         logger.debug("successfully generated GraphQL HTTP client")
diff --git a/plugins/graphql-kotlin-gradle-plugin/src/test/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLGradlePluginIT.kt b/plugins/graphql-kotlin-gradle-plugin/src/test/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLGradlePluginIT.kt
index 562dc2514d..0f274c2ec5 100755
--- a/plugins/graphql-kotlin-gradle-plugin/src/test/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLGradlePluginIT.kt
+++ b/plugins/graphql-kotlin-gradle-plugin/src/test/kotlin/com/expediagroup/graphql/plugin/gradle/GraphQLGradlePluginIT.kt
@@ -182,6 +182,7 @@ class GraphQLGradlePluginIT : GraphQLGradlePluginAbstractIT() {
             |    sdlEndpoint = "${wireMockServer.baseUrl()}/sdl"
             |    packageName = "com.example.generated"
             |    serializer = GraphQLSerializer.$serializer
+            |    useOptionalInputWrapper = true
             |  }
             |}
             """.trimMargin()
@@ -219,7 +220,8 @@ class GraphQLGradlePluginIT : GraphQLGradlePluginAbstractIT() {
                     mapOf(
                         "ktorClient" to useKtorClient,
                         "defaultHeader" to mapOf("name" to defaultHeaderName, "value" to defaultHeaderValue),
-                        "requestHeader" to mapOf("name" to customHeaderName, "value" to customHeaderValue)
+                        "requestHeader" to mapOf("name" to customHeaderName, "value" to customHeaderValue),
+                        "optionalInputWrapper" to (serializer == GraphQLSerializer.JACKSON)
                     )
                 )
             )
diff --git a/plugins/graphql-kotlin-gradle-plugin/src/test/resources/templates/Application.mustache b/plugins/graphql-kotlin-gradle-plugin/src/test/resources/templates/Application.mustache
index 47e5ac3b9c..465eb9e832 100644
--- a/plugins/graphql-kotlin-gradle-plugin/src/test/resources/templates/Application.mustache
+++ b/plugins/graphql-kotlin-gradle-plugin/src/test/resources/templates/Application.mustache
@@ -7,6 +7,7 @@ import com.example.generated.inputs.SimpleArgumentInput
 import com.example.generated.junitquery.BasicObject2
 import com.example.generated.junitquery.ScalarWrapper
 import com.example.generated.junitquery.SecondInterfaceImplementation
+{{#optionalInputWrapper}}import com.expediagroup.graphql.client.jackson.types.OptionalInput{{/optionalInputWrapper}}
 {{#ktorClient}}
 import com.expediagroup.graphql.client.ktor.GraphQLKtorClient
 {{#defaultHeader}}
@@ -48,7 +49,13 @@ fun main() {
     )
         {{/ktorClient}}
     {{/defaultHeader}}
-    val variables = JUnitQuery.Variables(SimpleArgumentInput(min = null, max = null, newName = "blah"))
+
+    {{#optionalInputWrapper}}
+    val variables = JUnitQuery.Variables(SimpleArgumentInput(newName = OptionalInput.Defined("blah")))
+    {{/optionalInputWrapper}}
+    {{^optionalInputWrapper}}
+    val variables = JUnitQuery.Variables(SimpleArgumentInput(newName = "blah"))
+    {{/optionalInputWrapper}}
     val query = JUnitQuery(variables)
 
     runBlocking {
diff --git a/plugins/graphql-kotlin-gradle-plugin/src/test/resources/templates/JUnit.mustache b/plugins/graphql-kotlin-gradle-plugin/src/test/resources/templates/JUnit.mustache
index d8ea9128d9..7d1dccafcf 100644
--- a/plugins/graphql-kotlin-gradle-plugin/src/test/resources/templates/JUnit.mustache
+++ b/plugins/graphql-kotlin-gradle-plugin/src/test/resources/templates/JUnit.mustache
@@ -31,7 +31,7 @@ class GraphQLMavenPluginTest {
         val graphQLEndpoint = System.getProperty("graphQLEndpoint")
         val client = GraphQLWebClient(graphQLEndpoint)
 
-        val variables = JUnitQuery.Variables(simpleCriteria = SimpleArgumentInput(min = null, max = null, newName = "blah"))
+        val variables = JUnitQuery.Variables(simpleCriteria = SimpleArgumentInput(newName = "blah"))
         val query = JUnitQuery(variables)
 
         assertDoesNotThrow {
diff --git a/plugins/graphql-kotlin-maven-plugin/README.md b/plugins/graphql-kotlin-maven-plugin/README.md
index 0995de0922..afd9af8898 100755
--- a/plugins/graphql-kotlin-maven-plugin/README.md
+++ b/plugins/graphql-kotlin-maven-plugin/README.md
@@ -46,6 +46,9 @@ Plugin should be configured as part of your `pom.xml` build file.
                     <connect>1000</connect>
                     <read>30000</read>
                 </timeoutConfiguration>
+                <!-- Opt-in flag to wrap nullable arguments in OptionalInput that distinguish between null and undefined value.
+                    Only supported for JACKSON serializer. -->
+                <useOptionalInputWrapper>false</useOptionalInputWrapper>
                 <queryFiles>
                     <queryFile>${project.basedir}/src/main/resources/queries/MyQuery.graphql</queryFile>
                 </queryFiles>
@@ -111,6 +114,7 @@ Generate GraphQL client code based on the provided GraphQL schema and target que
 | `queryFiles` | List<File> | | List of query files to be processed. Instead of a list of files to be processed you can also specify `queryFileDirectory` directory containing all the files. If this property is specified it will take precedence over the corresponding directory property. |
 | `serializer` | GraphQLSerializer | | JSON serializer that will be used to generate the data classes.<br/>**Default value is:** `GraphQLSerializer.JACKSON`. |
 | `schemaFile` | String | | GraphQL schema file that will be used to generate client code.<br/>**Default value is**: `${project.build.directory}/schema.graphql`<br/>**User property is**: `graphql.schemaFile`. |
+| `useOptionalInputWrapper` | Boolean | | Boolean opt-in flag to wrap nullable arguments in `OptionalInput` that distinguish between `null` and undefined/omitted value. Only supported for JACKSON serializer.<br/>**Default value is:** `false`.<br/>**User property is**: `graphql.useOptionalInputWrapper` |
 
 **Parameter Details**
 
@@ -131,6 +135,31 @@ Generate GraphQL client code based on the provided GraphQL schema and target que
     </customScalars>
     ```
 
+### generate-sdl
+
+Generates GraphQL schema in SDL format from your source code using reflections. Utilizes `graphql-kotlin-schema-generator`
+to generate the schema from classes implementing `graphql-kotlin-server` marker `Query`, `Mutation` and `Subscription` interfaces.
+In order to limit the amount of packages to scan, this mojo requires users to provide a list of `packages` that can contain
+GraphQL types.
+
+This MOJO utilizes [ServiceLoader](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/ServiceLoader.html)
+mechanism to dynamically load available `SchemaGeneratorHooksProvider` service providers from the classpath. Service provider
+can be provided as part of your project, included in one of your project dependencies or through explicitly provided artifact.
+See [Schema Generator Hooks Provider](./hooks-provider.mdx) for additional details on how to create custom hooks service
+provider. Configuration below shows how to configure GraphQL Kotlin plugin with explicitly provided artifact.
+
+**Attributes**
+
+* *Default Lifecycle Phase*: `process-classes`
+* *Requires Maven Project*
+
+**Parameters**
+
+| Property | Type | Required | Description |
+| -------- | ---- | -------- | ----------- |
+| `packages` | `List<String>` | yes | List of supported packages that can be scanned to generate SDL. |
+| `schemaFile` | File | | Target GraphQL schema file to be generated.<br/>**Default value is:** `${project.buildDir}/schema.graphql` |
+
 ### generate-test-client
 
 Generate GraphQL test client code based on the provided GraphQL schema and target queries.
@@ -153,6 +182,7 @@ Generate GraphQL test client code based on the provided GraphQL schema and targe
 | `queryFiles` | List<File> | | List of query files to be processed. Instead of a list of files to be processed you can also specify `queryFileDirectory` directory containing all the files. If this property is specified it will take precedence over the corresponding directory property. |
 | `serializer` | GraphQLSerializer | | JSON serializer that will be used to generate the data classes.<br/>**Default value is:** `GraphQLSerializer.JACKSON`. |
 | `schemaFile` | String | | GraphQL schema file that will be used to generate client code.<br/>**Default value is**: `${project.build.directory}/schema.graphql`<br/>**User property is**: `graphql.schemaFile`. |
+| `useOptionalInputWrapper` | Boolean | | Boolean opt-in flag to wrap nullable arguments in `OptionalInput` that distinguish between `null` and undefined/omitted value. Only supported for JACKSON serializer.<br/>**Default value is:** `false`.<br/>**User property is**: `graphql.useOptionalInputWrapper` |
 
 **Parameter Details**
 
diff --git a/plugins/graphql-kotlin-maven-plugin/src/integration/basic-setup/src/test/kotlin/com/expediagroup/graphql/plugin/maven/GraphQLMavenPluginTest.kt b/plugins/graphql-kotlin-maven-plugin/src/integration/basic-setup/src/test/kotlin/com/expediagroup/graphql/plugin/maven/GraphQLMavenPluginTest.kt
index cb0d35abe0..0ae1063723 100755
--- a/plugins/graphql-kotlin-maven-plugin/src/integration/basic-setup/src/test/kotlin/com/expediagroup/graphql/plugin/maven/GraphQLMavenPluginTest.kt
+++ b/plugins/graphql-kotlin-maven-plugin/src/integration/basic-setup/src/test/kotlin/com/expediagroup/graphql/plugin/maven/GraphQLMavenPluginTest.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2020 Expedia, Inc
+ * Copyright 2021 Expedia, Inc
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -53,7 +53,7 @@ class GraphQLMavenPluginTest {
         val graphQLEndpoint = System.getProperty("graphQLEndpoint")
         val client = GraphQLWebClient(graphQLEndpoint)
 
-        val variables = ExampleQuery.Variables(simpleCriteria = SimpleArgumentInput(newName = "whatever", min = null, max = null))
+        val variables = ExampleQuery.Variables(simpleCriteria = SimpleArgumentInput(newName = "whatever"))
         val query = ExampleQuery(variables)
         assertDoesNotThrow {
             runBlocking {
diff --git a/plugins/graphql-kotlin-maven-plugin/src/integration/complete-setup-jackson/pom.xml b/plugins/graphql-kotlin-maven-plugin/src/integration/complete-setup-jackson/pom.xml
index 1657659295..ecdd2a6720 100755
--- a/plugins/graphql-kotlin-maven-plugin/src/integration/complete-setup-jackson/pom.xml
+++ b/plugins/graphql-kotlin-maven-plugin/src/integration/complete-setup-jackson/pom.xml
@@ -100,6 +100,7 @@
                                 <queryFile>${project.basedir}/src/main/resources/DeprecatedQuery.graphql</queryFile>
                             </queryFiles>
                             <serializer>JACKSON</serializer>
+                            <useOptionalInputWrapper>true</useOptionalInputWrapper>
                         </configuration>
                     </execution>
                 </executions>
diff --git a/plugins/graphql-kotlin-maven-plugin/src/integration/complete-setup-jackson/src/test/kotlin/com/expediagroup/graphql/plugin/maven/GraphQLMavenPluginTest.kt b/plugins/graphql-kotlin-maven-plugin/src/integration/complete-setup-jackson/src/test/kotlin/com/expediagroup/graphql/plugin/maven/GraphQLMavenPluginTest.kt
index 95e890aae5..c8e95a6942 100755
--- a/plugins/graphql-kotlin-maven-plugin/src/integration/complete-setup-jackson/src/test/kotlin/com/expediagroup/graphql/plugin/maven/GraphQLMavenPluginTest.kt
+++ b/plugins/graphql-kotlin-maven-plugin/src/integration/complete-setup-jackson/src/test/kotlin/com/expediagroup/graphql/plugin/maven/GraphQLMavenPluginTest.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2020 Expedia, Inc
+ * Copyright 2021 Expedia, Inc
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,6 +23,7 @@ import com.expediagroup.graphql.plugin.generated.examplequery.SecondInterfaceImp
 import com.expediagroup.graphql.plugin.generated.examplequery.ScalarWrapper
 import com.expediagroup.graphql.plugin.generated.inputs.SimpleArgumentInput
 import com.expediagroup.graphql.plugin.generated.scalars.UUID
+import com.expediagroup.graphql.client.jackson.types.OptionalInput
 import com.expediagroup.graphql.client.spring.GraphQLWebClient
 import kotlinx.coroutines.runBlocking
 import org.junit.jupiter.api.Assertions.assertEquals
@@ -55,7 +56,7 @@ class GraphQLMavenPluginTest {
         val graphQLEndpoint = System.getProperty("graphQLEndpoint")
         val client = GraphQLWebClient(graphQLEndpoint)
 
-        val variables = ExampleQuery.Variables(simpleCriteria = SimpleArgumentInput(newName = "whatever", min = null, max = null))
+        val variables = ExampleQuery.Variables(simpleCriteria = SimpleArgumentInput(newName = OptionalInput.Defined("whatever")))
         val query = ExampleQuery(variables)
         assertDoesNotThrow {
             runBlocking {
diff --git a/plugins/graphql-kotlin-maven-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/maven/GenerateClientAbstractMojo.kt b/plugins/graphql-kotlin-maven-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/maven/GenerateClientAbstractMojo.kt
index f2420e532d..c5be2987ba 100644
--- a/plugins/graphql-kotlin-maven-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/maven/GenerateClientAbstractMojo.kt
+++ b/plugins/graphql-kotlin-maven-plugin/src/main/kotlin/com/expediagroup/graphql/plugin/maven/GenerateClientAbstractMojo.kt
@@ -92,6 +92,13 @@ abstract class GenerateClientAbstractMojo : AbstractMojo() {
     @Parameter(name = "serializer")
     private var serializer: GraphQLSerializer = GraphQLSerializer.JACKSON
 
+    /**
+     * Explicit opt-in flag to wrap nullable arguments in OptionalInput that supports both null and undefined values.
+     * Only supported for JACKSON serializer.
+     */
+    @Parameter(defaultValue = "\${graphql.useOptionalInputWrapper}", name = "useOptionalInputWrapper")
+    private var useOptionalInputWrapper: Boolean = false
+
     /**
      * Target directory where to store generated files.
      */
@@ -110,7 +117,7 @@ abstract class GenerateClientAbstractMojo : AbstractMojo() {
 
         logConfiguration(schemaPath, targetQueryFiles)
         val customGraphQLScalars = customScalars.map { GraphQLScalar(it.scalar, it.type, it.converter) }
-        generateClient(packageName, allowDeprecatedFields, customGraphQLScalars, serializer, schemaPath, targetQueryFiles).forEach {
+        generateClient(packageName, allowDeprecatedFields, customGraphQLScalars, serializer, schemaPath, targetQueryFiles, useOptionalInputWrapper).forEach {
             it.writeTo(outputDirectory)
         }
 
diff --git a/website/docs/plugins/gradle-plugin-tasks.mdx b/website/docs/plugins/gradle-plugin-tasks.mdx
index c7953ecadd..0614639cb2 100644
--- a/website/docs/plugins/gradle-plugin-tasks.mdx
+++ b/website/docs/plugins/gradle-plugin-tasks.mdx
@@ -139,6 +139,9 @@ graphql {
         // Read timeout in milliseconds
         read = 15_000
     }
+    // Opt-in flag to wrap nullable arguments in OptionalInput that distinguish between null and undefined value.
+    // Only supported for JACKSON serializer
+    useOptionalInputWrapper = false
   }
   schema {
     // List of supported packages that can contain GraphQL schema type definitions
@@ -181,6 +184,9 @@ graphql {
             t.connect = 5000
             t.read = 15000
         }
+        // Opt-in flag to wrap nullable arguments in OptionalInput that distinguish between null and undefined value.
+        // Only supported for JACKSON serializer
+        useOptionalInputWrapper = false
     }
     schema {
         packages = ["com.example"]
@@ -249,6 +255,7 @@ resulting generated code will be automatically added to the project main source
 | `serializer` | GraphQLSerializer | | JSON serializer that will be used to generate the data classes.<br/>**Default value is:** `GraphQLSerializer.JACKSON`. |
 | `schemaFile` | File | `schemaFileName` or `schemaFile` has to be provided | GraphQL schema file that will be used to generate client code. |
 | `schemaFileName` | String | `schemaFileName` or `schemaFile` has to be provided | Path to GraphQL schema file that will be used to generate client code.<br/>**Command line property is**: `schemaFileName`. |                                                                                                                                                     |
+| `useOptionalInputWrapper` | Boolean | | Boolean opt-in flag to wrap nullable arguments in `OptionalInput` that distinguish between `null` and undefined/omitted value. Only supported for JACKSON serializer.<br/>**Default value is:** `false`.<br/>**Command line property is**: `useOptionalInputWrapper` |
 
 By default, this task will generate Jackson compatible data models. See [client serialization documentation](../client/client-serialization.mdx)
 for details on how to update this process to use `kotlinx.serialization` instead.
@@ -298,6 +305,7 @@ test source set.
 | `serializer` | GraphQLSerializer | | JSON serializer that will be used to generate the data classes.<br/>**Default value is:** `GraphQLSerializer.JACKSON`. |
 | `schemaFile` | File | `schemaFileName` or `schemaFile` has to be provided | GraphQL schema file that will be used to generate client code. |
 | `schemaFileName` | String | `schemaFileName` or `schemaFile` has to be provided | Path to GraphQL schema file that will be used to generate client code.<br/>**Command line property is**: `schemaFileName`. |
+| `useOptionalInputWrapper` | Boolean | | Boolean opt-in flag to wrap nullable arguments in `OptionalInput` that distinguish between `null` and undefined/omitted value. Only supported for JACKSON serializer.<br/>**Default value is:** `false`.<br/>**Command line property is**: `useOptionalInputWrapper` |
 
 By default, this task will generate Jackson compatible data models. See [client serialization documentation](../client/client-serialization.mdx)
 for details on how to update this process to use `kotlinx.serialization` instead.
diff --git a/website/docs/plugins/maven-plugin-goals.md b/website/docs/plugins/maven-plugin-goals.md
index 8c622cfcdc..c7ab50752c 100644
--- a/website/docs/plugins/maven-plugin-goals.md
+++ b/website/docs/plugins/maven-plugin-goals.md
@@ -72,6 +72,7 @@ Generate GraphQL client code based on the provided GraphQL schema and target que
 | `queryFiles` | `List<File>` | | List of query files to be processed. Instead of a list of files to be processed you can also specify `queryFileDirectory` directory containing all the files. If this property is specified it will take precedence over the corresponding directory property. |
 | `serializer` | GraphQLSerializer | | JSON serializer that will be used to generate the data classes.<br/>**Default value is:** `GraphQLSerializer.JACKSON`. |
 | `schemaFile` | String | | GraphQL schema file that will be used to generate client code.<br/>**Default value is**: `${project.build.directory}/schema.graphql`<br/>**User property is**: `graphql.schemaFile`. |
+| `useOptionalInputWrapper` | Boolean | | Boolean opt-in flag to wrap nullable arguments in `OptionalInput` that distinguish between `null` and undefined/omitted value. Only supported for JACKSON serializer.<br/>**Default value is:** `false`.<br/>**User property is**: `graphql.useOptionalInputWrapper` |
 
 **Parameter Details**
 
@@ -139,6 +140,7 @@ Generate GraphQL test client code based on the provided GraphQL schema and targe
 | `queryFiles` | `List<File>` | | List of query files to be processed. Instead of a list of files to be processed you can also specify `queryFileDirectory` directory containing all the files. If this property is specified it will take precedence over the corresponding directory property. |
 | `serializer` | GraphQLSerializer | | JSON serializer that will be used to generate the data classes.<br/>**Default value is:** `GraphQLSerializer.JACKSON`. |
 | `schemaFile` | String | | GraphQL schema file that will be used to generate client code.<br/>**Default value is**: `${project.build.directory}/schema.graphql`<br/>**User property is**: `graphql.schemaFile`. |
+| `useOptionalInputWrapper` | Boolean | | Boolean opt-in flag to wrap nullable arguments in `OptionalInput` that distinguish between `null` and undefined/omitted value. Only supported for JACKSON serializer.<br/>**Default value is:** `false`.<br/>**User property is**: `graphql.useOptionalInputWrapper` |
 
 **Parameter Details**
 
diff --git a/website/docs/plugins/maven-plugin-usage.md b/website/docs/plugins/maven-plugin-usage.md
index 6f209fdfdf..42eba00ae1 100644
--- a/website/docs/plugins/maven-plugin-usage.md
+++ b/website/docs/plugins/maven-plugin-usage.md
@@ -313,7 +313,7 @@ Mojos will be executed in the order they are defined in your `pom.xml` build fil
 ## Complete Configuration Example
 
 Following is a configuration example that downloads schema SDL from a target GraphQL server that is then used to generate
-the GraphQL client data modles using `kotlinx.serialization` that are based on the provided query.
+the GraphQL client data models using `kotlinx.serialization` that are based on the provided query.
 
 ```xml
 <project>