Bug 125420 [Commands] parameters: allow commands to specify return type
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/Command.java
* information to <code>System.out</code> when executing.
	 */
	public static boolean DEBUG_COMMAND_EXECUTION = false;
	/**
	 * This flag can be set to <code>true</code> if commands should print
	 * information to <code>System.out</code> when changing handlers.
	 */
	public static boolean DEBUG_HANDLERS = false;
	/**
	 * This flag can be set to a particular command identifier if only that
	 * command should print information to <code>System.out</code> when
	 * changing handlers.
	 */
	public static String DEBUG_HANDLERS_COMMAND_ID = null;
	/**
	 * The category to which this command belongs. This value should not be
	 * <code>null</code> unless the command is undefined.
	 */
	private Category category = null;
	/**
	 * A collection of objects listening to the execution of this command. This
	 * collection is <code>null</code> if there are no listeners.
	 */
	private transient ListenerList executionListeners = null;
	/**
	 * The handler currently associated with this command. This value may be
	 * <code>null</code> if there is no handler currently.
	 */
	private transient IHandler handler = null;
	/**