This bug report concerns the following file:

debugger.jpda.ui/src/org/netbeans/modules/debugger/jpda/ui/WatchPanel.java

This file contains the class org.netbeans.modules.debugger.jpda.ui.WatchPanel.MyTrees which extends com.sun.source.util.Trees.

The latter has a new abstract method getLub(com.sun.source.tree.CatchTree) in Java 7, see:

http://download.oracle.com/javase/7/docs/jdk/api/javac/tree/com/sun/source/util/Trees.html

This appears to be fixed by adding the following method, although I am unsure of the consequences of doing so:

 @Override
 public TypeMirror getLub(CatchTree tree) {
     return trees.getLub(tree);
 }