code: def backfill_fields(self, fields, forms):
          
          if forms and not fields:
              new_fields = [self.def_field]
          elif fields and self.def_field not in fields:
              new_fields = list(fields)
              if self.def_field not in fields:
                  new_fields.append(self.def_field)
          elif not fields:
              new_fields = self.field_names
          else:
              new_fields = list(fields)
          return new_fields
docs: Properly backfill fields to explicitly request specific
          keys. The issue is that >6.X servers *only* return requested fields
          so to improve backwards compatiblity for PyCap clients, add specific fields
          when required.
  
          Parameters
          ----------
          fields: list
              requested fields
          forms: list
              requested forms
  
          Returns
          -------
              new fields, forms