docs: def to_json(self, drop_null=True, camel=False, indent=None, sort_keys=False):
          """Serialize self as JSON
  
          Args:
              drop_null: bool, default True. Remove 'empty' attributes. See
                  to_dict.
              camel: bool, default True. Convert keys to camelCase.
              indent: int, default None. See json built-in.
              sort_keys: bool, default False. See json built-in.
  
          Return:
              str: object params.
          """
          return json.dumps(self.to_dict(drop_null, camel), indent=indent,
                            sort_keys=sort_keys)