Check the underlying type

src/AutoMapper/ConfigurationValidator.cs

@@ -85,10 +85,16 @@ private void DryRunTypeMap(ICollection<TypeMap> typeMapsChecked, TypePair types,
                 }
                 var context = new ValidationContext(types, propertyMap, mapperToUse);
                 _config.Validate(context);
-                if (mapperToUse is ArrayMapper || mapperToUse is EnumerableMapper || mapperToUse is CollectionMapper)
+                if(mapperToUse is ArrayMapper || mapperToUse is EnumerableMapper || mapperToUse is CollectionMapper)
                 {
                     CheckElementMaps(typeMapsChecked, types, propertyMap);
                 }
+                else if(mapperToUse is NullableSourceMapper)
+                {
+                    var newTypePair = new TypePair(Nullable.GetUnderlyingType(types.SourceType), types.DestinationType);
+                    var memberTypeMap = _config.ResolveTypeMap(newTypePair.SourceType, newTypePair.DestinationType);
+                    DryRunTypeMap(typeMapsChecked, newTypePair, memberTypeMap, propertyMap);
+                }
             }
         }
 
@@ -119,8 +125,7 @@ private void CheckPropertyMaps(ICollection<TypeMap> typeMapsChecked, TypeMap typ
                     return;
 
                 var destinationType = propertyMap.DestinationProperty.GetMemberType();
-                var memberTypeMap = _config.ResolveTypeMap(sourceType,
-                    destinationType);
+                var memberTypeMap = _config.ResolveTypeMap(sourceType, destinationType);
 
                 if (typeMapsChecked.Any(tm => Equals(tm, memberTypeMap)))
                     continue;

src/UnitTests/Bug/NullableToInvalid.cs

@@ -0,0 +1,34 @@
+using System;
+using Should;
+using Xunit;
+
+namespace AutoMapper.UnitTests.Bug
+{
+    public class NullableToInvalid : NonValidatingSpecBase
+    {
+        public class Source
+        {
+            public int? Value { get; set; }
+        }
+
+        public class Destination
+        {
+            public SomeObject Value { get; set; }
+        }
+
+        public class SomeObject
+        {
+        }
+
+        protected override MapperConfiguration Configuration { get; } = new MapperConfiguration(cfg =>
+        {
+            cfg.CreateMap<Source, Destination>();
+        });
+
+        [Fact]
+        public void Should_not_validate()
+        {
+            new Action(Configuration.AssertConfigurationIsValid).ShouldThrow<AutoMapperConfigurationException>();
+        }
+    }
+}

src/UnitTests/UnitTests.Net4.csproj

@@ -86,6 +86,7 @@
     <Compile Include="AssertionExtensions.cs" />
     <Compile Include="BasicFlattening.cs" />
     <Compile Include="Bug\CannotProjectStringToNullableEnum.cs" />
+    <Compile Include="Bug\NullableToInvalid.cs" />
     <Compile Include="Bug\OneSourceWithMultipleDestinationsAndPreserveReferences.cs" />
     <Compile Include="Bug\ConventionCreateMapsWithCircularReference.cs" />
     <Compile Include="Bug\ConvertMapperThreading.cs" />