Bug 125420 [Commands] parameters: allow commands to specify return type
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/Command.java
* The ordered array of parameters understood by this command. This value
	 * may be <code>null</code> if there are no parameters, or if the command
	 * is undefined. It may also be empty.
	 */
	private IParameter[] parameters = null;
	/**
	 * Constructs a new instance of <code>Command</code> based on the given
	 * identifier. When a command is first constructed, it is undefined.
	 * Commands should only be constructed by the <code>CommandManager</code>
	 * to ensure that the identifier remains unique.
	 * 
	 * @param id
	 *            The identifier for the command. This value must not be
	 *            <code>null</code>, and must be unique amongst all commands.
	 */
	Command(final String id) {
		super(id);
	}
	/**
	 * Adds a listener to this command that will be notified when this command's
	 * state changes.
	 * 
	 * @param commandListener
	 *            The listener to be added; must not be <code>null</code>.
	 */
	public final void addCommandListener(final ICommandListener commandListener) {
		if (commandListener == null) {
			throw new NullPointerException("Cannot add a null command listener"); 
		}
		addListenerObject(commandListener);