code: public Deferred execute(final GwtCommand command, final CommandCallback... callback) {
  		final Deferred deferred = new Deferred();
  		for (CommandCallback successCallback : callback) {
  			try {
  				deferred.addCallback(successCallback);
  			} catch (Throwable t) {
  				Log.logError("Command failed on success callback", t);
  			}
  		}
  		return execute(command, deferred);
  	}
docs: The execution function. Executes a server side command.
  
  @param command
  The command to be executed. This command is a wrapper around the actual request object.
  @param callback
  A <code>CommandCallback</code> function to be executed when the command successfully returns. The
  callbacks may implement CommunicationExceptionCallback or CommandExceptionCallback to allow error
  handling.
  @return deferred object which can be used to add extra callbacks