Make isEmpty a getter.

utils/pub/command_help.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library command_help;
 
 import 'pub.dart';
 
 /** Handles the `help` pub command. */
 class HelpCommand extends PubCommand {
   String get description => "display help information for Pub";
   String get usage => 'pub help [command]';
   bool get requiresEntrypoint => false;
 
   Future onRun() {
-    if (commandOptions.rest.isEmpty()) {
+    if (commandOptions.rest.isEmpty) {
       printUsage();
     } else {
       pubCommands[commandOptions.rest[0]].printUsage();
     }
   }
 }