Errors with tag and %find with improper content

If accidently MongoDB keywords with $ are used in tags and searches the following exceptions occur: pymongo.errors.WriteError, pymongo.errors.OperationFailure: $and must be an array, full error: {'ok': 0.0, 'errmsg': '$and must be an array', 'code': 2, 'codeName': 'BadValue'}. They cause crashes. Maybe we should catch all pymongo errors accordingly?