code: def parse_json(self, req, name, field):
          
          json_data = self._cache.get("json")
          if json_data is None:
              try:
                  self._cache["json"] = json_data = core.parse_json(req.body, req.charset)
              except json.JSONDecodeError as e:
                  if e.doc == "":
                      return core.missing
                  else:
                      return self.handle_invalid_json_error(e, req)
              if json_data is None:
                  return core.missing
          return core.get_value(json_data, name, field, allow_many_nested=True)
docs: Pull a json value from the request.