Remove reflection handling for kotlin.Unit class

There is just enough to check the value type name against "kotlin.Unit" literal.
This way we don't need extra reflection bits to be exposed into a native image

Author: artembilan

spring-integration-core/src/main/java/org/springframework/integration/aot/CoreRuntimeHints.java

@@ -100,8 +100,7 @@ public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
 
 		Stream.of(
 						"kotlin.jvm.functions.Function0",
-						"kotlin.jvm.functions.Function1",
-						"kotlin.Unit")
+						"kotlin.jvm.functions.Function1")
 				.forEach(type ->
 						reflectionHints.registerTypeIfPresent(classLoader, type, MemberCategory.INVOKE_PUBLIC_METHODS));
 

spring-integration-core/src/main/java/org/springframework/integration/util/ClassUtils.java

@@ -84,11 +84,6 @@ public abstract class ClassUtils {
 	 */
 	public static final Class<?> KOTLIN_FUNCTION_1_CLASS;
 
-	/**
-	 * The {@code kotlin.Unit} class object.
-	 */
-	public static final Class<?> KOTLIN_UNIT_CLASS;
-
 	static {
 		PRIMITIVE_WRAPPER_TYPE_MAP.put(Boolean.class, boolean.class);
 		PRIMITIVE_WRAPPER_TYPE_MAP.put(Byte.class, byte.class);
@@ -166,23 +161,11 @@ public abstract class ClassUtils {
 			finally {
 				KOTLIN_FUNCTION_1_CLASS = kotlinClass;
 			}
-
-			kotlinClass = null;
-			try {
-				kotlinClass = org.springframework.util.ClassUtils.forName("kotlin.Unit", defaultClassLoader);
-			}
-			catch (ClassNotFoundException e) {
-				//Ignore: assume no Kotlin in classpath
-			}
-			finally {
-				KOTLIN_UNIT_CLASS = kotlinClass;
-			}
 		}
 		else {
 			KOTLIN_FUNCTION_0_CLASS = null;
 			KOTLIN_FUNCTION_0_INVOKE_METHOD = null;
 			KOTLIN_FUNCTION_1_CLASS = null;
-			KOTLIN_UNIT_CLASS = null;
 		}
 	}
 
@@ -278,7 +261,7 @@ public static boolean isKotlinFunction1(Class<?> aClass) {
 	 * @since 5.3.2
 	 */
 	public static boolean isKotlinUnit(Class<?> aClass) {
-		return KOTLIN_UNIT_CLASS != null && KOTLIN_UNIT_CLASS.isAssignableFrom(aClass);
+		return "kotlin.Unit".equals(aClass.getName());
 	}
 
 }