Bug 125420 [Commands] parameters: allow commands to specify return type
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/Command.java
"There is no handler to execute."); 
		fireNotHandled(e);
		throw e;
	}
	/**
	 * Notifies the listeners for this command that it has changed in some way.
	 * 
	 * @param commandEvent
	 *            The event to send to all of the listener; must not be
	 *            <code>null</code>.
	 */
	private final void fireCommandChanged(final CommandEvent commandEvent) {
		if (commandEvent == null) {
			throw new NullPointerException("Cannot fire a null event"); 
		}
		final Object[] listeners = getListeners();
		for (int i = 0; i < listeners.length; i++) {
			final ICommandListener listener = (ICommandListener) listeners[i];
			listener.commandChanged(commandEvent);
		}
	}
	/**
	 * Notifies the execution listeners for this command that an attempt to
	 * execute has failed because the command is not defined.
	 * 
	 * @param e
	 *            The exception that is about to be thrown; never
	 *            <code>null</code>.
	 * @since 3.2
	 */