/** Singleton placeholder that indicates a value is being loaded. */
  @SuppressWarnings("unchecked") // impl never uses a parameter or returns any non-null value
  static <K, V> ValueReference<K, V> unset() {
    return (ValueReference<K, V>) UNSET;
  }

  private enum NullEntry implements ReferenceEntry<Object, Object> {
    INSTANCE;

    @Override
    public @Nullable ValueReference<Object, Object> getValueReference() {

	// MINIO_KMS_SECRET_KEY_FILE - either to the argument passed to
	// the container or to a default string (e.g. "minio_master_key").
	//
	// We have to distinguish a explicit config from an implicit. Hence,
	// we unset the env. vars if they are set but empty or contain a path
	// which does not exist. The downside of this check is that if
	// MINIO_KMS_SECRET_KEY_FILE is set to a path that does not exist,

* `path` - The file path to the file to stream.
* `headers` - Any custom headers to include, as a dictionary.
* `media_type` - A string giving the media type. If unset, the filename or path will be used to infer a media type.
* `filename` - If set, this will be included in the response `Content-Disposition`.

// the file it describes, it may be necessary to modify the Name field
// of the returned header to provide the full path name of the file.
// If compression is desired, callers should set the FileHeader.Method
// field; it is unset by default.
func FileInfoHeader(fi fs.FileInfo) (*FileHeader, error) {
	size := fi.Size()
	fh := &FileHeader{
		Name:               fi.Name(),
		UncompressedSize64: uint64(size),
	}
	fh.SetModTime(fi.ModTime())

		gorootPath = runtime.GOROOT()
		if gorootPath != "" {
			return
		}

		// runtime.GOROOT is empty — perhaps go_android_exec was built with
		// -trimpath and GOROOT is unset. Try 'go env GOROOT' as a fallback,
		// assuming that the 'go' command in $PATH is the correct one.

		cmd := exec.Command("go", "env", "GOROOT")
		cmd.Stderr = os.Stderr
		out, err := cmd.Output()
		if err != nil {

### Use the `response_model_exclude_unset` parameter { #use-the-response-model-exclude-unset-parameter }

You can set the *path operation decorator* parameter `response_model_exclude_unset=True`:

{* ../../docs_src/response_model/tutorial004_py310.py hl[22] *}

### Use o parâmetro `response_model_exclude_unset` { #use-the-response-model-exclude-unset-parameter }

Você pode definir o parâmetro `response_model_exclude_unset=True` do *decorador de operação de rota*:

{* ../../docs_src/response_model/tutorial004_py310.py hl[22] *}

### Den `response_model_exclude_unset`-Parameter verwenden { #use-the-response-model-exclude-unset-parameter }

Sie können den *Pfadoperation-Dekorator*-Parameter `response_model_exclude_unset=True` setzen:

{* ../../docs_src/response_model/tutorial004_py310.py hl[22] *}

### Используйте параметр `response_model_exclude_unset` { #use-the-response-model-exclude-unset-parameter }

Вы можете установить у *декоратора операции пути* параметр `response_model_exclude_unset=True`:

{* ../../docs_src/response_model/tutorial004_py310.py hl[22] *}

                    if (downloadMonitor != null) {
                        wagon.addTransferListener(downloadMonitor);
                    }
                }

                // unset the firstRun flag, so we don't get caught in an infinite loop...
                firstRun = false;
            }
        } catch (ConnectionException e) {