Bug 249574 [Contributions] ExternalActionManager.addPropertyChangeListener() doesn't register the ListenerList
bundles/org.eclipse.jface/src/org/eclipse/jface/action/ExternalActionManager.java
*            The callback mechanism for checking whether a command is
		 *            active; must not be <code>null</code>.
		 * @param checker
		 *            The callback to check if an IAction should fire execution
		 *            events.
		 * 
		 * @since 3.4
		 */
		public CommandCallback(final BindingManager bindingManager,
				final CommandManager commandManager,
				final IActiveChecker activeChecker,
				final IExecuteApplicable checker) {
			if (bindingManager == null) {
				throw new NullPointerException(
						"The callback needs a binding manager"); 
			}
			if (commandManager == null) {
				throw new NullPointerException(
						"The callback needs a command manager"); 
			}
			if (activeChecker == null) {
				throw new NullPointerException(
						"The callback needs an active callback"); 
			}
			if (checker == null) {
				throw new NullPointerException(
						"The callback needs an applicable callback"); 
			}
			this.activeChecker = activeChecker;
			this.bindingManager = bindingManager;