Revert to old behavior of Optional mapping by default

Author: vojtapol

src/main/kotlin/graphql/kickstart/tools/MethodFieldResolver.kt

@@ -92,11 +92,10 @@ internal class MethodFieldResolver(
                 }
 
                 if (value == null && isOptional) {
-                    if (environment.containsArgument(definition.name)) {
-                        return@add Optional.empty<Any>()
-                    } else {
+                    if (options.inputArgumentOptionalNullWhenOmitted && !environment.containsArgument(definition.name)) {
                         return@add null
                     }
+                    return@add Optional.empty<Any>()
                 }
 
                 if (value != null

src/main/kotlin/graphql/kickstart/tools/SchemaParserOptions.kt

@@ -25,6 +25,7 @@ data class SchemaParserOptions internal constructor(
     val allowUnimplementedResolvers: Boolean,
     val objectMapperProvider: PerFieldObjectMapperProvider,
     val proxyHandlers: List<ProxyHandler>,
+    val inputArgumentOptionalNullWhenOmitted: Boolean,
     val preferGraphQLResolver: Boolean,
     val introspectionEnabled: Boolean,
     val coroutineContextProvider: CoroutineContextProvider,
@@ -50,6 +51,7 @@ data class SchemaParserOptions internal constructor(
         private var allowUnimplementedResolvers = false
         private var objectMapperProvider: PerFieldObjectMapperProvider = PerFieldConfiguringObjectMapperProvider()
         private val proxyHandlers: MutableList<ProxyHandler> = mutableListOf(Spring4AopProxyHandler(), GuiceAopProxyHandler(), JavassistProxyHandler(), WeldProxyHandler())
+        private var inputArgumentOptionalNullWhenOmitted = false
         private var preferGraphQLResolver = false
         private var introspectionEnabled = true
         private var coroutineContextProvider: CoroutineContextProvider? = null
@@ -80,6 +82,10 @@ data class SchemaParserOptions internal constructor(
             this.allowUnimplementedResolvers = allowUnimplementedResolvers
         }
 
+        fun inputArgumentOptionalNullWhenOmitted(inputArgumentOptionalNullWhenOmitted: Boolean) = this.apply {
+            this.inputArgumentOptionalNullWhenOmitted = inputArgumentOptionalNullWhenOmitted
+        }
+
         fun preferGraphQLResolver(preferGraphQLResolver: Boolean) = this.apply {
             this.preferGraphQLResolver = preferGraphQLResolver
         }
@@ -146,9 +152,18 @@ data class SchemaParserOptions internal constructor(
                 genericWrappers
             }
 
-            return SchemaParserOptions(contextClass, wrappers, allowUnimplementedResolvers, objectMapperProvider,
-                proxyHandlers, preferGraphQLResolver, introspectionEnabled, coroutineContextProvider,
-                typeDefinitionFactories, fieldVisibility
+            return SchemaParserOptions(
+                contextClass,
+                wrappers,
+                allowUnimplementedResolvers,
+                objectMapperProvider,
+                proxyHandlers,
+                inputArgumentOptionalNullWhenOmitted,
+                preferGraphQLResolver,
+                introspectionEnabled,
+                coroutineContextProvider,
+                typeDefinitionFactories,
+                fieldVisibility
             )
         }
     }