Fix default value of --output-chartjson-data '' -> None

build/android/test_runner.py

 #!/usr/bin/env python
 #
 # Copyright 2013 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.
 
 """Runs all types of tests from one unified interface."""
 
 import argparse
 import collections
@@ skipping 558 matching lines @@
 
   group.add_argument(
       '--output-json-list', type=os.path.realpath,
       help='Write a simple list of names from --steps into the given file.')
   group.add_argument(
       '--collect-chartjson-data',
       action='store_true',
       help='Cache the chartjson output from each step for later use.')
   group.add_argument(
       '--output-chartjson-data',
-      default='',
       type=os.path.realpath,
       help='Write out chartjson into the given file.')
   # TODO(rnephew): Remove this when everything moves to new option in platform
   # mode.
   group.add_argument(
       '--get-output-dir-archive', metavar='FILENAME', type=os.path.realpath,
       help='Write the cached output directory archived by a step into the'
       ' given ZIP file.')
   group.add_argument(
       '--output-dir-archive-path', metavar='FILENAME', type=os.path.realpath,
@@ skipping 360 matching lines @@
     if e.is_infra_error:
       return constants.INFRA_EXIT_CODE
     return constants.ERROR_EXIT_CODE
   except: # pylint: disable=W0702
     logging.exception('Unrecognized error occurred.')
     return constants.ERROR_EXIT_CODE
 
 
 if __name__ == '__main__':
   sys.exit(main())