if (value == null) {
        tryDrainReferenceQueues();
        return null;
      }

      return value;
    }

    /**
     * Performs routine cleanup following a read. Normally cleanup happens during writes, or from
     * the cleanupExecutor. If cleanup is not observed after a sufficient number of reads, try
     * cleaning up from the read thread.
     */
    void postReadCleanup() {

            throw new SmbException("Invalid operation for workgroups, servers, or shares");
        }

        try (SmbTreeHandleImpl th = ensureTreeConnected()) {
            // should not normally be required, but samba without NTStatus does not properly resolve the path and fails
            // with
            // STATUS_UNSUCCESSFUL
            exists();

        connect0();

        if (LogStream.level >= 3) {
            log.println("queryPath: " + path);
        }

        /* normally we'd check the negotiatedCapabilities for CAP_NT_SMBS
         * however I can't seem to get a good last modified time from
         * SMB_COM_QUERY_INFORMATION so if NT_SMBs are requested

## Die normale **FastAPI**-Anwendung

Sehen wir uns zunächst an, wie die normale API-Anwendung aussehen würde, bevor wir den Callback hinzufügen.

Sie verfügt über eine *Pfadoperation*, die einen `Invoice`-Body empfängt, und einen Query-Parameter `callback_url`, der die URL für den Callback enthält.

Dieser Teil ist ziemlich normal, der größte Teil des Codes ist Ihnen wahrscheinlich bereits bekannt:

   *     cancelled regardless
   * @return {@code false} if the step could not be cancelled, typically because it has already
   *     completed normally; {@code true} otherwise
   */
  @CanIgnoreReturnValue
  @SuppressWarnings("Interruption") // We are propagating an interrupt from a caller.
  public boolean cancel(boolean mayInterruptIfRunning) {

### Andere Hilfsfunktionen

      certificatePinnerBuilder.add(
        server.hostName,
        pin(certificate),
      )
    }
    response1.body.close()

    // Make another request with certificate pinning. It should complete normally.
    client =
      client
        .newBuilder()
        .certificatePinner(certificatePinnerBuilder.build())
        .build()
    val request2 = Request.Builder().url(server.url("/")).build()

### Lanzar excepciones

Estas dependencias pueden `raise` excepciones, igual que las dependencias normales:

{* ../../docs_src/dependencies/tutorial006_an_py39.py hl[10,15] *}

### Valores de retorno

Y pueden devolver valores o no, los valores no serán usados.

Así que, puedes reutilizar una dependencia normal (que devuelve un valor) que ya uses en otro lugar, y aunque el valor no se use, la dependencia será ejecutada:

If <code>D</code> returns normally, without starting a new
<code>panic</code>, the panicking sequence stops. In that case,
the state of functions called between <code>G</code> and the call to <code>panic</code>
is discarded, and normal execution resumes.
Any functions deferred by <code>G</code> before <code>D</code> are then run and <code>G</code>'s

    * This allows adding extra code after a dependency is done. It can be used, for example, to close database connections.
    * Dependencies with `yield` can be normal or `async`, **FastAPI** will run normal dependencies in a threadpool.
    * They can be combined with normal dependencies.
    * It's possible to have arbitrary trees/levels of dependencies with `yield` and exit steps are handled in the correct order automatically.