fix(oneof-anyof-nulls): added fix for deserializing null values to oaf containers (#59)

This commit adds support for the null values to pass while deserialization if none of the inner types are matched as the OAF containers are nullable by default

Author: asadali214

APIMatic.Core.Test/Utilities/OneOfContainerTest.cs

@@ -78,6 +78,14 @@ public void TestNativeType()
                     });
         }
 
+        [Test]
+        public void TestNativeTypeWithNullValue()
+        {
+            NativeOneOfContainer container = CoreHelper.JsonDeserialize<NativeOneOfContainer>("null");
+
+            Assert.IsNull(container);
+        }
+
         [Test]
         public void TestNativeNullableType()
         {

APIMatic.Core/Utilities/Converters/UnionTypeConverter.cs

@@ -79,6 +79,12 @@ private T DeserializeOneOfAnyOf(JToken token, JsonSerializer serializer, List<Un
                 return mappedValues[0].value;
             }
 
+            if (token.Type == JTokenType.Null)
+            {
+                // allow null values to pass as the OAF containers are nullable by default
+                return default;
+            }
+
             if (_isOneOf)
             {
                 throw new OneOfValidationException(unMappedTypes, token.ToString());