Allow an empty "dependencies" key in a pubspec.

utils/tests/pub/pubspec_test.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 pubspec_test;
 
 import '../../../pkg/unittest/lib/unittest.dart';
 import '../../pub/pubspec.dart';
 import '../../pub/source.dart';
 import '../../pub/source_registry.dart';
@@ skipping 23 matching lines @@
     version: ">=1.2.3 <3.4.5"
 ''', sources);
 
         var foo = pubspec.dependencies[0];
         expect(foo.name, equals('foo'));
         expect(foo.constraint.allows(new Version(1, 2, 3)), isTrue);
         expect(foo.constraint.allows(new Version(1, 2, 5)), isTrue);
         expect(foo.constraint.allows(new Version(3, 4, 5)), isFalse);
       });
 
+      test("allows an empty dependencies map", () {
+        var pubspec = new Pubspec.parse('''
+dependencies:
+''', sources);
+
+        expect(pubspec.dependencies, isEmpty);
+      });
+
       test("throws if the description isn't valid", () {
         expect(() {
           new Pubspec.parse('''
 dependencies:
   foo:
     mock: bad
 ''', sources);
         }, throwsFormatException);
       });
 
@@ skipping 45 matching lines @@
 # Including for completeness
 # ...and hoping the spec expands to include details about author, version, etc
 # See http://www.dartlang.org/docs/pub-package-manager/ for details
 ''', sources);
         expect(pubspec.version, equals(Version.none));
         expect(pubspec.dependencies, isEmpty);
       });
     });
   });
 }