Treat empty string DartPackage as no DartPackage specified

mojo/dart/tools/presubmit/check_mojom_dart.py

 #!/usr/bin/env python
 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Checks that released mojom.dart files in the source tree are up to date"""
 
 import argparse
 import os
 import subprocess
@@ skipping 38 matching lines @@
   namespace = mojom.namespace
   elements = ['lib']
   elements.extend(namespace.split('.'))
   elements.append("%s.dart" % name)
   return os.path.join(*elements)
 
 
 # Given a mojom.Module, return the package or None.
 def _mojom_package(mojom):
   if mojom.attributes:
-    return mojom.attributes.get('DartPackage')
+    package = mojom.attributes.get('DartPackage')
+    if package == None:
+      return package
+    package = package.strip()
+    if package == '':
+      return None
+    return package
 
 # Load and parse a .mojom file. Returns the mojom.Module or raises an Exception
 # if there was an error.
 def _load_mojom(path_to_mojom):
   filename = os.path.abspath(path_to_mojom)
 
   # Parse
   mojom_file_graph = parser_runner.ParseToMojomFileGraph(SDK_DIR, [filename],
       meta_data_only=True)
   if mojom_file_graph is None:
@@ skipping 355 matching lines @@
   if args.affected_files:
     check_failure = presubmit_check(packages, args.affected_files)
   else:
     check_failure = global_check(packages)
   if check_failure:
     return 2
   return 0
 
 if __name__ == '__main__':
     sys.exit(main())