Merge pull request #24629 from andrey4623

* pr/24629:
  Polish "Make a field final"
  Make a field final

Closes gh-24629

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/config/StandardConfigDataResource.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -36,7 +36,7 @@ public class StandardConfigDataResource extends ConfigDataResource {
 
 	private final Resource resource;
 
-	private boolean emptyDirectory;
+	private final boolean emptyDirectory;
 
 	/**
 	 * Create a new {@link StandardConfigDataResource} instance.