svndiff.py: properly handle empty expectations dictionary

tools/jsondiff.py

 #!/usr/bin/python
 
 '''
 Copyright 2013 Google Inc.
 
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 '''
 
 '''
@@ skipping 62 matching lines @@
 
         Any tests which violate those assumptions will cause an exception to
         be raised.
 
         Any tests for which we have no expectations will be left out of the
         returned dictionary.
         """
         result_dict = {}
         json_dict = gm_json.LoadFromString(contents)
         all_expectations = json_dict[gm_json.JSONKEY_EXPECTEDRESULTS]
+
+        # Prevent https://code.google.com/p/skia/issues/detail?id=1588
+        # ('svndiff.py: 'NoneType' object has no attribute 'keys'')
+        if not all_expectations:
+            return result_dict
+
         for test_name in all_expectations.keys():
             test_expectations = all_expectations[test_name]
             allowed_digests = test_expectations[
                 gm_json.JSONKEY_EXPECTEDRESULTS_ALLOWEDDIGESTS]
             if allowed_digests:
                 num_allowed_digests = len(allowed_digests)
                 if num_allowed_digests > 1:
                     raise ValueError(
                         'test %s has %d allowed digests' % (
                             test_name, num_allowed_digests))
@@ skipping 93 matching lines @@
         'ACTUAL results from the "old" JSON file. This can be a ' +
         'filepath on local storage, or a URL.')
     args = parser.parse_args()
     differ = GMDiffer()
     diffs = differ.GenerateDiffDict(oldfile=args.old, newfile=args.new)
     json.dump(diffs, sys.stdout, sort_keys=True, indent=2)
 
 
 if __name__ == '__main__':
     _Main()