Bug 534517 - Configure JRE doesnt work from JDK compliance preference
page ( and NPE later)

Change-Id: Ic572ca93951b4033e589b6f33ce0d095847e25b2
diff --git a/org.eclipse.jdt.debug.ui/ui/org/eclipse/jdt/internal/debug/ui/jres/JREsPreferencePage.java b/org.eclipse.jdt.debug.ui/ui/org/eclipse/jdt/internal/debug/ui/jres/JREsPreferencePage.java
index 0a6ba6c..0dd221c 100644
--- a/org.eclipse.jdt.debug.ui/ui/org/eclipse/jdt/internal/debug/ui/jres/JREsPreferencePage.java
+++ b/org.eclipse.jdt.debug.ui/ui/org/eclipse/jdt/internal/debug/ui/jres/JREsPreferencePage.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2018 IBM Corporation and others.
+ * Copyright (c) 2000, 2020 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -338,7 +338,9 @@
 	@Override
 	public void dispose() {
 		super.dispose();
-		fJREBlock.dispose();
+		if (fJREBlock != null) {
+			fJREBlock.dispose();
+		}
 	}
 
 	/*