code: def rectify_multipart_form_data(self, data):
          
          for name, field in self.base_fields.items():
              try:
                  field.implode_multi_values(name, data)
              except AttributeError:
                  pass
          return data
docs: If a widget was converted and the Form data was submitted through a multipart request,
          then these data fields must be converted to suit the Django Form validation