docs: def _build_environ(self) -> Dict[str, Optional[str]]:
          """
          Build environment variables suitable for passing to the Model.
          """
          d: Dict[str, Optional[str]] = {}
  
          if self.__config__.case_insensitive:
              env_vars = {k.lower(): v for k, v in os.environ.items()}
          else:
              env_vars = cast(Dict[str, str], os.environ)
  
          for field in self.__fields__.values():
              if field.has_alias:
                  env_name = field.alias
              else:
                  env_name = self.__config__.env_prefix + field.name.upper()
  
              env_name_ = env_name.lower() if self.__config__.case_insensitive else env_name
              env_val = env_vars.get(env_name_, None)
  
              if env_val:
                  if field.is_complex():
                      try:
                          env_val = json.loads(env_val)
                      except ValueError as e:
                          raise SettingsError(f'error parsing JSON for "{env_name}"') from e
                  d[field.alias] = env_val
          return d