old_contents: import json
  import decimal
  import datetime
  from bson.dbref import DBRef
  from bson.objectid import ObjectId
  from mongoengine.base import BaseDocument
  
  isbound = lambda m: getattr(m, 'im_self', None) is not None
  
  class MongoEncoder(json.JSONEncoder):
      def default(self, value, **kwargs):
          if isinstance(value, ObjectId):
              return unicode(value)
          elif isinstance(value, DBRef):
              return value.id
          if isinstance(value, datetime.datetime):
              return value.isoformat()
          if isinstance(value, datetime.date):
              return value.strftime("%Y-%m-%d")
          if isinstance(value, decimal.Decimal):
              return str(value)
          return json.JSONEncoder.default(value, **kwargs)
  
new_contents: import json
  import decimal
  import datetime
  from bson.dbref import DBRef
  from bson.objectid import ObjectId
  from mongoengine.base import BaseDocument
  
  isbound = lambda m: getattr(m, 'im_self', None) is not None
  
  class MongoEncoder(json.JSONEncoder):
      def default(self, value, **kwargs):
          if isinstance(value, ObjectId):
              return unicode(value)
          elif isinstance(value, DBRef):
              return value.id
          if isinstance(value, datetime.datetime):
              return value.isoformat()
          if isinstance(value, datetime.date):
              return value.strftime("%Y-%m-%d")
          if isinstance(value, decimal.Decimal):
              return str(value)
          return super(MongoEncoder, self).default(value, **kwargs)
  
subject: Fix bad call to superclass method