consistent use of JDK 1.5's ThreadLocal.remove() over ThreadLocal.set(null), preventing leaks (SPR-7441)

org.springframework.jdbc/src/main/java/org/springframework/jdbc/datasource/UserCredentialsDataSourceAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2009 the original author or authors.
+ * Copyright 2002-2010 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.
@@ -114,7 +114,7 @@ public class UserCredentialsDataSourceAdapter extends DelegatingDataSource {
 	 * @see #setCredentialsForCurrentThread
 	 */
 	public void removeCredentialsFromCurrentThread() {
-		this.threadBoundCredentials.set(null);
+		this.threadBoundCredentials.remove();
 	}