der wichtigste Teil ist, um einen Parameter optional zu machen, da dieses `None` der Defaultwert ist, und das ist es, was diesen Parameter **nicht erforderlich** macht.

Der Teil mit `Union[str, None]` erlaubt es Ihrem Editor, Sie besser zu unterstützen, aber er sagt FastAPI nicht, dass dieser Parameter optional ist.

///

Jetzt können wir `Query` weitere Parameter übergeben. Fangen wir mit dem `max_length` Parameter an, der auf Strings angewendet wird:

```

as it will use that `None` as the default value, and that way make the parameter **not required**.

The `Union[str, None]` part allows your editor to provide better support, but it is not what tells FastAPI that this parameter is not required.

///

Then, we can pass more parameters to `Query`. In this case, the `max_length` parameter that applies to strings:

```Python

        // Parameters
        // ----------------------------------------------------------------------

        PlexusConfiguration[] parameterConfigurations = c.getChild("parameters").getChildren("parameter");

        List<Parameter> parameters = new ArrayList<>();

        for (PlexusConfiguration d : parameterConfigurations) {
            Parameter parameter = new Parameter();

///

### Deklarieren Sie einen *Pfad-Parameter*

Dann erstellen Sie einen *Pfad-Parameter*, der als Typ die gerade erstellte Enum-Klasse hat (`ModelName`):

```Python hl_lines="16"
{!../../docs_src/path_params/tutorial005.py!}
```

### Testen Sie es in der API-Dokumentation

 * types, and also for interfaces and public classes that have public parameter-less constructors.
 * When the non-null default value for a particular parameter type cannot be provided by {@code
 * NullPointerTester}, the caller can provide a custom non-null default value for the parameter type
 * via {@link #setDefault}.
 *
 * @author Kevin Bourrillion
 * @since 10.0
 */
@GwtIncompatible

   * the dummy value of a constructor or method parameter is unknown.
   */
  @VisibleForTesting
  static class ParameterNotInstantiableException extends Exception {
    public ParameterNotInstantiableException(Parameter parameter) {
      super(
          "Cannot determine value for parameter "
              + parameter
              + " of "
              + parameter.getDeclaringInvokable());
    }
  }

  /**

If you pass a "callable" as a dependency in **FastAPI**, it will analyze the parameters for that "callable", and process them in the same way as the parameters for a *path operation function*. Including sub-dependencies.

That also applies to callables with no parameters at all. The same as it would be for *path operation functions* with no parameters.

     * Set the value of hostname, used in parameter comment. <br>
     * Even if empty string, treated as empty plainly. So "IF pmb != null" is false if empty.
     * @param hostname The parameter value of hostname. (NotNull)
     */
    public void setHostname(String hostname) {
        registerVariable("hostname", hostname);
    }

    /**
     * Set the value of jobname, used in parameter comment. <br>

        </field>
      </fields>
    </class>

    <class xdoc.anchorName="parameter">
      <name>Parameter</name>
      <version>1.0.0+</version>
      <description>A parameter description.</description>
      <!-- see o.a.m.plugin.descriptor.Parameter -->
      <fields>
        <field>
          <name>name</name>
          <version>1.0.0+</version>

        final String parameter = request.getParameter(parameterKey);
        if (logger.isDebugEnabled()) {
            logger.debug("{}:{}", parameterKey, parameter);
        }
        if (StringUtil.isNotEmpty(parameter)) {
            parseRoleSet(parameter, encryptedParameterValue, roleSet);
        }

    }