Bug 87856 [Commands] Last closed editor leaked due to reference by command manager
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/Command.java
*            state of the application; must not be <code>null</code>.
	 * @return The result of the execution; may be <code>null</code>.
	 * @throws ExecutionException
	 *             If the handler has problems executing this command.
	 * @throws NotHandledException
	 *             If there is no handler.
	 */
	public final Object execute(final ExecutionEvent event)
			throws ExecutionException, NotHandledException {
		final IHandler handler = this.handler;
		
		if (DEBUG_COMMAND_EXECUTION) {
			System.out.print("COMMANDS >>> executing ");  
			if (handler == null) {
				System.out.print("no handler"); 
			} else {
				System.out.print('\''); 
				System.out.print(handler.getClass().getName());
				System.out.print("'("); 
				System.out.print(handler.hashCode());
				System.out.print(')'); 
			}
			System.out.println();
		}
		
		if ((handler != null) && (handler.isHandled()))
			return handler.execute(event);
		throw new NotHandledException("There is no handler to execute."); 
	}
	/**