Merge pull request #426 from holunda-io/feature/add_kotlin_docs

Add docs for kotlin usage #394

README.md

@@ -182,6 +182,11 @@ public class ApproveOrderTaskControllerTest {
 }
 ```
 
+### Kotlin
+
+If you use kotlin, there is an own collection of factory methods by simple using `CamundaBpmDataKotlin` instead of `CamundaBpmData`.
+For usage examples, see here: [Examples Kotlin](https://www.holunda.io/camunda-bpm-data/snapshot/user-guide/examples-kotlin.html)
+
 ### Further documentation
 
 For further details, please consult our [Quick Start](https://www.holunda.io/camunda-bpm-data/snapshot/quick-start)

docs/user-guide/examples-kotlin.md

@@ -15,6 +15,23 @@ object Variables {
 }
 ```
 
+### Define nonNull variable
+
+**IMPORTANT:** Since 1.5.0 all predefined variable types are nullable by default. (For more information, see  here: [Github Issue](https://github.com/holunda-io/camunda-bpm-data/issues/394))
+If you want to define a variable to be non-null-able, please call nonNull on variable factory as shown in the example below.
+
+``` kotlin
+
+import io.holunda.data.CamundaBpmDataKotlin
+
+object Variables {
+    val ORDER_ID: VariableFactory<String> = stringVariable("orderId").nonNull
+    val CUSTOMER_ID: VariableFactory<String?> = stringVariable("orderId")
+}
+```
+
+## 
+
 ## Read variable from Java delegate
 
 ``` kotlin