Bug 125420 [Commands] parameters: allow commands to specify return type
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/Command.java
}
		}
		final NotHandledException e = new NotHandledException(
				"There is no handler to execute."); 
		fireNotHandled(e);
		throw e;
	}
	/**
	 * Executes this command by delegating to the current handler, if any. If
	 * the debugging flag is set, then this method prints information about
	 * which handler is selected for performing this command. This does checks
	 * to see if the command is enabled and defined. If it is not both enabled
	 * and defined, then the execution listeners will be notified and an
	 * exception thrown.
	 * 
	 * @param event
	 *            An event containing all the information about the current
	 *            state of the application; must not be <code>null</code>.
	 * @return The result of the execution; may be <code>null</code>. This
	 *         result will be available to the client executing the command, and
	 *         execution listeners.
	 * @throws ExecutionException
	 *             If the handler has problems executing this command.
	 * @throws NotDefinedException
	 *             If the command you are trying to execute is not defined.
	 * @throws NotEnabledException
	 *             If the command you are trying to execute is not enabled.
	 * @throws NotHandledException
	 *             If there is no handler.
	 * @since 3.2