Bug 218467 [Undo] Tighten up IUndoableOperation spec and AbstractOperation to discourage/prevent null labels
GMF creates CompositeCommands with null labels. These NPE when shortenText(getOperation().getLabel()) is invoked from update.
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/IUndoableOperation.java
* IUndoContext#matches(IUndoContext)}) another context.
	 * 
	 * @param context
	 *            the context to be removed
	 */
	void removeContext(IUndoContext context);
	/**
	 * Undo the operation. This method should only be called after an operation
	 * has been executed.
	 * 
	 * @param monitor
	 *            the progress monitor (or <code>null</code>) to use for
	 *            reporting progress to the user.
	 * @param info
	 *            the IAdaptable (or <code>null</code>) provided by the
	 *            caller in order to supply UI information for prompting the
	 *            user if necessary. When this parameter is not
	 *            <code>null</code>, it should minimally contain an adapter
	 *            for the org.eclipse.swt.widgets.Shell.class.
	 * @return the IStatus of the undo. The status severity should be set to
	 *         <code>OK</code> if the redo was successful, and
	 *         <code>ERROR</code> if it was not. Any other status is assumed
	 *         to represent an incompletion of the undo.
	 * @throws ExecutionException
	 *             if an exception occurred during undo.
	 */
	IStatus undo(IProgressMonitor monitor, IAdaptable info)
			throws ExecutionException;
}