diff --git a/spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java b/spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java
index b33b8721b13..6e2916f1a4a 100644
--- a/spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java
+++ b/spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java
@@ -321,7 +321,8 @@ public class InvocableHandlerMethod extends HandlerMethod {
 						Object arg = args[index];
 						if (!(parameter.isOptional() && arg == null)) {
 							KType type = parameter.getType();
-							if (!(type.isMarkedNullable() && arg == null) && type.getClassifier() instanceof KClass<?> kClass
+							if (!(type.isMarkedNullable() && arg == null)
+									&& type.getClassifier() instanceof KClass<?> kClass
 									&& KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(kClass))) {
 								arg = box(kClass, arg);
 							}
@@ -341,7 +342,8 @@ public class InvocableHandlerMethod extends HandlerMethod {
 		private static Object box(KClass<?> kClass, @Nullable Object arg) {
 			KFunction<?> constructor = Objects.requireNonNull(KClasses.getPrimaryConstructor(kClass));
 			KType type = constructor.getParameters().get(0).getType();
-			if (!(type.isMarkedNullable() && arg == null) && type.getClassifier() instanceof KClass<?> parameterClass
+			if (!(type.isMarkedNullable() && arg == null)
+					&& type.getClassifier() instanceof KClass<?> parameterClass
 					&& KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(parameterClass))) {
 				arg = box(parameterClass, arg);
 			}
diff --git a/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java b/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java
index 9bea3c8f5fa..2effeb2ee2d 100644
--- a/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java
+++ b/spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java
@@ -360,7 +360,8 @@ public class InvocableHandlerMethod extends HandlerMethod {
 							Object arg = args[index];
 							if (!(parameter.isOptional() && arg == null)) {
 								KType type = parameter.getType();
-								if (!(type.isMarkedNullable() && arg == null) && type.getClassifier() instanceof KClass<?> kClass
+								if (!(type.isMarkedNullable() && arg == null)
+										&& type.getClassifier() instanceof KClass<?> kClass
 										&& KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(kClass))) {
 									arg = box(kClass, arg);
 								}
@@ -378,10 +379,11 @@ public class InvocableHandlerMethod extends HandlerMethod {
 			}
 		}
 
-		private static Object box(KClass<?> kClass, Object arg) {
+		private static Object box(KClass<?> kClass, @Nullable Object arg) {
 			KFunction<?> constructor = Objects.requireNonNull(KClasses.getPrimaryConstructor(kClass));
 			KType type = constructor.getParameters().get(0).getType();
-			if (!(type.isMarkedNullable() && arg == null) && type.getClassifier() instanceof KClass<?> parameterClass
+			if (!(type.isMarkedNullable() && arg == null)
+					&& type.getClassifier() instanceof KClass<?> parameterClass
 					&& KotlinDetector.isInlineClass(JvmClassMappingKt.getJavaClass(parameterClass))) {
 				arg = box(parameterClass, arg);
 			}