Support nullable Kotlin value class arguments

This commit skips the value class parameter instantiation for nullable
types when a null argument is passed.

Closes gh-32353

spring-core/src/main/java/org/springframework/core/CoroutinesUtils.java

@@ -115,18 +115,20 @@ public abstract class CoroutinesUtils {
 						switch (parameter.getKind()) {
 							case INSTANCE -> argMap.put(parameter, target);
 							case VALUE, EXTENSION_RECEIVER -> {
-								if (!parameter.isOptional() || args[index] != null) {
+								Object arg = args[index];
+								if (!(parameter.isOptional() && arg == null)) {
 									if (parameter.getType().getClassifier() instanceof KClass<?> kClass) {
 										Class<?> javaClass = JvmClassMappingKt.getJavaClass(kClass);
-										if (KotlinDetector.isInlineClass(javaClass)) {
-											argMap.put(parameter, KClasses.getPrimaryConstructor(kClass).call(args[index]));
+										if (KotlinDetector.isInlineClass(javaClass)
+												&& !(parameter.getType().isMarkedNullable() && arg == null)) {
+											argMap.put(parameter, KClasses.getPrimaryConstructor(kClass).call(arg));
 										}
 										else {
-											argMap.put(parameter, args[index]);
+											argMap.put(parameter, arg);
 										}
 									}
 									else {
-										argMap.put(parameter, args[index]);
+										argMap.put(parameter, arg);
 									}
 								}
 								index++;

spring-core/src/test/kotlin/org/springframework/core/CoroutinesUtilsTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -82,6 +82,15 @@ class CoroutinesUtilsTests {
 			.verify()
 	}
 
+	@Test
+	fun invokeSuspendingFunctionWithNullableParameter() {
+		val method = CoroutinesUtilsTests::class.java.getDeclaredMethod("suspendingFunctionWithNullable", String::class.java, Continuation::class.java)
+		val mono = CoroutinesUtils.invokeSuspendingFunction(method, this, null, null) as Mono
+		runBlocking {
+			Assertions.assertThat(mono.awaitSingleOrNull()).isNull()
+		}
+	}
+
 	@Test
 	fun invokeNonSuspendingFunction() {
 		val method = CoroutinesUtilsTests::class.java.getDeclaredMethod("nonSuspendingFunction", String::class.java)
@@ -165,6 +174,15 @@ class CoroutinesUtilsTests {
 		}
 	}
 
+	@Test
+	fun invokeSuspendingFunctionWithNullableValueClassParameter() {
+		val method = CoroutinesUtilsTests::class.java.declaredMethods.first { it.name.startsWith("suspendingFunctionWithNullableValueClass") }
+		val mono = CoroutinesUtils.invokeSuspendingFunction(method, this, null, null) as Mono
+		runBlocking {
+			Assertions.assertThat(mono.awaitSingleOrNull()).isNull()
+		}
+	}
+
 	@Test
 	fun invokeSuspendingFunctionWithExtension() {
 		val method = CoroutinesUtilsTests::class.java.getDeclaredMethod("suspendingFunctionWithExtension",
@@ -190,6 +208,11 @@ class CoroutinesUtilsTests {
 		return value
 	}
 
+	suspend fun suspendingFunctionWithNullable(value: String?): String? {
+		delay(1)
+		return value
+	}
+
 	suspend fun suspendingFunctionWithFlow(): Flow<String> {
 		delay(1)
 		return flowOf("foo", "bar")
@@ -222,6 +245,11 @@ class CoroutinesUtilsTests {
 		return value.value
 	}
 
+	suspend fun suspendingFunctionWithNullableValueClass(value: ValueClass?): String? {
+		delay(1)
+		return value?.value
+	}
+
 	suspend fun CustomException.suspendingFunctionWithExtension(): String {
 		delay(1)
 		return "${this.message}"

spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java

@@ -313,18 +313,20 @@ public class InvocableHandlerMethod extends HandlerMethod {
 				switch (parameter.getKind()) {
 					case INSTANCE -> argMap.put(parameter, target);
 					case VALUE, EXTENSION_RECEIVER -> {
-						if (!parameter.isOptional() || args[index] != null) {
+						Object arg = args[index];
+						if (!(parameter.isOptional() && arg == null)) {
 							if (parameter.getType().getClassifier() instanceof KClass<?> kClass) {
 								Class<?> javaClass = JvmClassMappingKt.getJavaClass(kClass);
-								if (KotlinDetector.isInlineClass(javaClass)) {
-									argMap.put(parameter, KClasses.getPrimaryConstructor(kClass).call(args[index]));
+								if (KotlinDetector.isInlineClass(javaClass)
+										&& !(parameter.getType().isMarkedNullable() && arg == null)) {
+									argMap.put(parameter, KClasses.getPrimaryConstructor(kClass).call(arg));
 								}
 								else {
-									argMap.put(parameter, args[index]);
+									argMap.put(parameter, arg);
 								}
 							}
 							else {
-								argMap.put(parameter, args[index]);
+								argMap.put(parameter, arg);
 							}
 						}
 						index++;

spring-web/src/test/kotlin/org/springframework/web/method/support/InvocableHandlerMethodKotlinTests.kt

@@ -105,6 +105,13 @@ class InvocableHandlerMethodKotlinTests {
 		Assertions.assertThatIllegalArgumentException().isThrownBy { invocable.invokeForRequest(request, null) }
 	}
 
+	@Test
+	fun valueClassWithNullable() {
+		composite.addResolver(StubArgumentResolver(LongValueClass::class.java, null))
+		val value = getInvocable(ValueClassHandler::class.java, LongValueClass::class.java).invokeForRequest(request, null)
+		Assertions.assertThat(value).isNull()
+	}
+
 	@Test
 	fun propertyAccessor() {
 		val value = getInvocable(PropertyAccessorHandler::class.java).invokeForRequest(request, null)
@@ -173,6 +180,9 @@ class InvocableHandlerMethodKotlinTests {
 		fun valueClassWithInit(valueClass: ValueClassWithInit) =
 			valueClass
 
+		fun valueClassWithNullable(limit: LongValueClass?) =
+			limit?.value
+
 	}
 
 	private class PropertyAccessorHandler {

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java

@@ -324,18 +324,20 @@ public class InvocableHandlerMethod extends HandlerMethod {
 					switch (parameter.getKind()) {
 						case INSTANCE -> argMap.put(parameter, target);
 						case VALUE, EXTENSION_RECEIVER -> {
-							if (!parameter.isOptional() || args[index] != null) {
+							Object arg = args[index];
+							if (!(parameter.isOptional() && arg == null)) {
 								if (parameter.getType().getClassifier() instanceof KClass<?> kClass) {
 									Class<?> javaClass = JvmClassMappingKt.getJavaClass(kClass);
-									if (KotlinDetector.isInlineClass(javaClass)) {
-										argMap.put(parameter, KClasses.getPrimaryConstructor(kClass).call(args[index]));
+									if (KotlinDetector.isInlineClass(javaClass)
+											&& !(parameter.getType().isMarkedNullable() && arg == null)) {
+										argMap.put(parameter, KClasses.getPrimaryConstructor(kClass).call(arg));
 									}
 									else {
-										argMap.put(parameter, args[index]);
+										argMap.put(parameter, arg);
 									}
 								}
 								else {
-									argMap.put(parameter, args[index]);
+									argMap.put(parameter, arg);
 								}
 							}
 							index++;

spring-webflux/src/test/kotlin/org/springframework/web/reactive/result/InvocableHandlerMethodKotlinTests.kt

@@ -19,7 +19,6 @@ package org.springframework.web.reactive.result
 import io.mockk.every
 import io.mockk.mockk
 import kotlinx.coroutines.delay
-import org.assertj.core.api.Assertions
 import org.assertj.core.api.Assertions.assertThat
 import org.junit.jupiter.api.Test
 import org.springframework.core.MethodParameter
@@ -178,11 +177,19 @@ class InvocableHandlerMethodKotlinTests {
 
 	@Test
 	fun nullReturnValue() {
-		val method = NullResultController::nullable.javaMethod!!
+		val method = NullResultController::nullableReturnValue.javaMethod!!
 		val result = invoke(NullResultController(), method)
 		assertHandlerResultValue(result, null)
 	}
 
+	@Test
+	fun nullParameter() {
+		this.resolvers.add(stubResolver(null, String::class.java))
+		val method = NullResultController::nullableParameter.javaMethod!!
+		val result = invoke(NullResultController(), method, null)
+		assertHandlerResultValue(result, null)
+	}
+
 	@Test
 	fun valueClass() {
 		this.resolvers.add(stubResolver(1L, Long::class.java))
@@ -192,7 +199,7 @@ class InvocableHandlerMethodKotlinTests {
 	}
 
 	@Test
-	fun valueClassDefaultValue() {
+	fun valueClassWithDefaultValue() {
 		this.resolvers.add(stubResolver(null, Double::class.java))
 		val method = ValueClassController::valueClassWithDefault.javaMethod!!
 		val result = invoke(ValueClassController(), method)
@@ -207,6 +214,14 @@ class InvocableHandlerMethodKotlinTests {
 		assertExceptionThrown(result, IllegalArgumentException::class)
 	}
 
+	@Test
+	fun valueClassWithNullable() {
+		this.resolvers.add(stubResolver(null, LongValueClass::class.java))
+		val method = ValueClassController::valueClassWithNullable.javaMethod!!
+		val result = invoke(ValueClassController(), method, null)
+		assertHandlerResultValue(result, "null")
+	}
+
 	@Test
 	fun propertyAccessor() {
 		this.resolvers.add(stubResolver(null, String::class.java))
@@ -321,9 +336,13 @@ class InvocableHandlerMethodKotlinTests {
 		fun unit() {
 		}
 
-		fun nullable(): String? {
+		fun nullableReturnValue(): String? {
 			return null
 		}
+
+		fun nullableParameter(value: String?): String? {
+			return value
+		}
 	}
 
 	class ValueClassController {
@@ -337,6 +356,9 @@ class InvocableHandlerMethodKotlinTests {
 		fun valueClassWithInit(valueClass: ValueClassWithInit) =
 			valueClass
 
+		fun valueClassWithNullable(limit: LongValueClass?) =
+			"${limit?.value}"
+
 	}
 
 	class PropertyAccessorController {