"error": {
       "message": "AttributeError: Failed to process datasource.lower_case(<english.informals.revision.parent.matches>):
'NoneType' object has no attribute 'lower'\nTraceback (most recent call last):\n
 File \"/srv/deployment/ores/venv/lib/python3.4/site-packages/revscoring/dependencies/functions.py\", line 244, in _solve\n    value = dependent(*args)\n
 File \"/srv/deployment/ores/venv/lib/python3.4/site-packages/revscoring/dependencies/dependent.py\", line 52, in __call__\n    return self.process(*args, **kwargs)\n
 File \"/srv/deployment/ores/venv/lib/python3.4/site-packages/revscoring/datasources/meta/mappers.py\", line 35, in process\n    return [self.apply(item) for item in items]\n
 File \"/srv/deployment/ores/venv/lib/python3.4/site-packages/revscoring/datasources/meta/mappers.py\", line 35, in <listcomp>\n    return [self.apply(item) for item in items]\n
 File \"/srv/deployment/ores/venv/lib/python3.4/site-packages/revscoring/datasources/meta/mappers.py\", line 54, in lower\n    return s.lower()\nAttributeError: 'NoneType' object has no attribute 'lower'\n",
       "type": "CaughtDependencyError"
     }
   }