Upgrade error mediagoblin

gistfile1.txt

sh-4.3$ python --version
Python 2.7.8
sh-4.3$ ./bin/gmg dbupdate
/usr/lib/python2.7/dist-packages/gi/module.py:178: Warning: g_array_append_vals: assertion 'array' failed
  g_type = info.get_g_type()
/usr/lib/python2.7/dist-packages/gi/module.py:178: Warning: g_hash_table_lookup: assertion 'hash_table != NULL' failed
  g_type = info.get_g_type()
/usr/lib/python2.7/dist-packages/gi/module.py:178: Warning: g_hash_table_insert_internal: assertion 'hash_table != NULL' failed
  g_type = info.get_g_type()
WARNING: audiolab is not installed so wav2png will not work
/usr/local/mediagoblin/mediagoblin/local/lib/python2.7/site-packages/SQLAlchemy-0.8.6-py2.7-linux-i686.egg/sqlalchemy/engine/default.py:471: SAWarning: Unicode type received non-unicode bind param value.
-> Updating plugin "mediagoblin.media_types.video":
   + Running migration 3, "change_metadata_format"... Traceback (most recent call last):
  File "./bin/gmg", line 9, in <module>
    load_entry_point('mediagoblin==0.8.1.dev', 'console_scripts', 'gmg')()
  File "/usr/local/mediagoblin/mediagoblin/mediagoblin/gmg_commands/__init__.py", line 142, in main_cli
    args.func(args)
  File "/usr/local/mediagoblin/mediagoblin/mediagoblin/gmg_commands/dbupdate.py", line 160, in dbupdate
    run_dbupdate(app_config, global_config)
  File "/usr/local/mediagoblin/mediagoblin/mediagoblin/gmg_commands/dbupdate.py", line 128, in run_dbupdate
    run_all_migrations(db, app_config, global_config)
  File "/usr/local/mediagoblin/mediagoblin/mediagoblin/gmg_commands/dbupdate.py", line 155, in run_all_migrations
    migration_manager.init_or_migrate()
  File "/usr/local/mediagoblin/mediagoblin/mediagoblin/db/migration_tools.py", line 288, in init_or_migrate
    migration_func(self.session)
  File "/usr/local/mediagoblin/mediagoblin/mediagoblin/media_types/video/migrations.py", line 62, in change_metadata_format
    metadata = json.loads(row.orig_metadata)
  File "/usr/lib/python2.7/json/__init__.py", line 338, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python2.7/json/decoder.py", line 366, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
TypeError: expected string or buffer