for (int i = 0; i < nodeList.getLength(); i++) {
                        final Node node = nodeList.item(i);
                        final NamedNodeMap attributes = node.getAttributes();
                        if (attributes != null) {
                            final Node classAttr = attributes.getNamedItem("class");
                            if (classAttr != null) {

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: Union[bool, None] = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}


@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):

            if (!tag.equals("inheritDoc")) {
                return false;
            }
            for (Node node : source.getCommentText()) {
                nodeStack.appendChild(node);
            }
            return true;
        }
    }

    private interface CommentSource {
        Iterable<? extends Node> getCommentText();
    }

    private static class NoOpCommentSource implements CommentSource {

      // GWT's HashMap.entrySet().removeAll(null) doesn't throws NPE.
    }
  }

  @Override
  public void testEntrySetRetainAllNullFromEmpty() {
    try {
      super.testEntrySetRetainAllNullFromEmpty();
    } catch (RuntimeException tolerated) {
      // GWT's HashMap.entrySet().retainAll(null) doesn't throws NPE.
    }
  }

  @Override
  public void testKeySetRemoveAllNullFromEmpty() {

</div>

This means that it will **always have a value**, it's just that sometimes the value could be `None` (or `null` in JSON).

That means that, clients using your API don't have to check if the value exists or not, they can **assume the field will always be there**, but just that in some cases it will have the default value of `None`.

The way to describe this in OpenAPI, is to mark that field as **required**, because it will always be there.

from docs_src.header_params.tutorial003_an import app

client = TestClient(app)


@pytest.mark.parametrize(
    "path,headers,expected_status,expected_response",
    [
        ("/items", None, 200, {"X-Token values": None}),
        ("/items", {"x-token": "foo"}, 200, {"X-Token values": ["foo"]}),
        # TODO: fix this, is it a bug?

   * serialized with XML 1.0.
   *
   * <p>For SOAP 1.1 messages, see {@code XML_UTF_8} per <a
   * href="http://www.w3.org/TR/2000/NOTE-SOAP-20000508/">W3C Note on Simple Object Access Protocol
   * (SOAP) 1.1</a>
   *
   * @since 20.0
   */
  public static final MediaType SOAP_XML_UTF_8 = createConstantUtf8(APPLICATION_TYPE, "soap+xml");

import java.util.AbstractSet;
import java.util.Map;
import javax.annotation.CheckForNull;

/**
 * A class to represent the set of edges connecting an (implicit) origin node to a target node.
 *
 * <p>The {@link #nodeToOutEdge} map means this class only works on networks without parallel edges.
 * See {@link MultiEdgesConnecting} for a class that works with parallel edges.
 *
 * @author James Sexton

    <offline>true</offline>
    ]]></configuration>
      <description>
        <![CDATA[
      Flags the system as offline, to prevent accessing the network to resolve artifacts or execute plugins.

      NOTE: It's also possible to switch to offline mode on a per-build basis, using the '-o' command-line option.
    ]]></description>
    </expression>
    <expression>
      <syntax>settings.interactiveMode</syntax>

      AbstractNetworkTest.validateNetwork(network);

      Collections.shuffle(nodeList, gen);
      for (Integer node : nodeList) {
        assertThat(network.addNode(node)).isTrue();
      }
      Collections.shuffle(edgeList, gen);
      for (Object edge : edgeList) {
        assertThat(
                network.addEdge(