Prevent unnecessary unboxing

See gh-40985

Author: asashour

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/tomcat/NestedJarResourceSet.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -128,7 +128,7 @@ protected boolean isMultiRelease() {
 				}
 			}
 		}
-		return this.multiRelease.booleanValue();
+		return this.multiRelease;
 	}
 
 	@Override