```python
from typing import Optional


def say_hi(name: Optional[str]):
    print(f"Hey {name}!")
```

The parameter `name` is defined as `Optional[str]`, but it is **not optional**, you cannot call the function without the parameter:

```Python
say_hi()  # Oh, no, this throws an error! 😱
```

The `name` parameter is **still required** (not *optional*) because it doesn't have a default value. Still, `name` accepts `None` as the value:

Als Teil der Erstellung des Anwendungsobjekts wird eine *Pfadoperation* für `/openapi.json` (oder welcher Wert für den Parameter `openapi_url` gesetzt wurde) registriert.

                if (oldNullability && !newNullability) {
                    errors << "Parameter $idx from null accepting to non-null accepting breaking change".toString()
                } else if (!oldNullability && newNullability) {
                    warnings << "Parameter $idx nullability changed from non-nullable to nullable".toString()
                }
            }
        }

     *             installation has failed
     * @throws IllegalArgumentException if {@code request} is {@code null} or parameter
     *             {@code localRepository} is {@code null} or {@code localRepository} is not a directory
     *             or parameter {@code mavenArtifacts} is {@code null} or
     *             {@code mavenArtifacts.isEmpty()} is {@code true}.
     */

            fail("Initialize should not throw exception with valid annotation: " + e.getMessage());
        }
    }

    // Test parameter validation without relying on complex configuration
    @Test
    public void test_validateParameters_basic() {
        // Test that parameter validation can be performed
        final CustomSize validAnnotation = createBasicAnnotation();

        try {

      </plugin>
      <plugin>
        <groupId>com.github.siom79.japicmp</groupId>
        <artifactId>japicmp-maven-plugin</artifactId>
        <configuration>
          <parameter>
            <excludes>

import org.jspecify.annotations.Nullable;

/**
 * An implementation of {@link NetworkConnections} for undirected networks with parallel edges.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 */
final class UndirectedMultiNetworkConnections<N, E>
    extends AbstractUndirectedNetworkConnections<N, E> {

  private UndirectedMultiNetworkConnections(Map<E, N> incidentEdges) {

        <artifactId>japicmp-maven-plugin</artifactId>
        <configuration>
          <parameter>
            <excludes>
              <exclude>org.apache.maven.plugin.lifecycle</exclude>
              <exclude>org.apache.maven.plugin.descriptor.PluginDescriptor#getLifecycleMapping(java.lang.String)</exclude>
            </excludes>
          </parameter>
        </configuration>
      </plugin>
    </plugins>
  </build>

///

## Datenklassen in `response_model` { #dataclasses-in-response-model }

Sie können `dataclasses` auch im Parameter `response_model` verwenden:

{* ../../docs_src/dataclasses_/tutorial002_py310.py hl[1,6:12,18] *}

Die Datenklasse wird automatisch in eine Pydantic-Datenklasse konvertiert.

///

## Dataclasses in `response_model` { #dataclasses-in-response-model }

You can also use `dataclasses` in the `response_model` parameter:

{* ../../docs_src/dataclasses_/tutorial002_py310.py hl[1,6:12,18] *}

The dataclass will be automatically converted to a Pydantic dataclass.

This way, its schema will show up in the API docs user interface: