code: def to_native(self, value):
          
          if isinstance(value, dict):
              return value
          elif isinstance(value, six.string_types):
              native_value = json.loads(value)
              if isinstance(native_value, dict):
                  return native_value
              else:
                  raise ConversionError(u'Cannot load value as a dict: {}'.format(value))
docs: Return the value as a dict, raising error if conversion to dict is not possible