* also be non-null.
   *
   * <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will
   * silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the graph.
   *
   * <p>If {@code edge} already connects {@code nodeU} to {@code nodeV} (in the specified order if

/** Reuse a connection from the pool. */
internal class ReusePlan(
  val connection: RealConnection,
) : RoutePlanner.Plan {
  override val isReady = true

  override fun connectTcp() = error("already connected")

  override fun connectTlsEtc() = error("already connected")

  override fun handleSuccess() = connection

  override fun cancel() = error("unexpected cancel")

            FailedPlan(e)
          }
        }
        else -> return null // Nothing further to try.
      }

    // Already connected. Return it immediately.
    if (plan.isReady) return ConnectResult(plan)

    // Already failed? Return it immediately.
    if (plan is FailedPlan) return plan.result

    // Connect TCP asynchronously.
    tcpConnectsInFlight += plan

   * also be non-null.
   *
   * <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will
   * silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the graph.
   *
   * <p>If {@code edge} already connects {@code nodeU} to {@code nodeV} (in the specified order if

          required: true
        - label: I already searched in Google "How to X in FastAPI" and didn't find any information.
          required: true
        - label: I already read and followed all the tutorial in the docs and didn't find an answer.
          required: true
        - label: I already checked if it is not related to FastAPI but to [Pydantic](https://github.com/pydantic/pydantic).

  /**
   * Adds {@code node} if it is not already present.
   *
   * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
   *
   * @return {@code true} if the graph was modified as a result of this call
   */
  @CanIgnoreReturnValue
  boolean addNode(N node);

  /**
   * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present, and sets

## Development

By the time I started creating **FastAPI** itself, most of the pieces were already in place, the design was defined, the requirements and tools were ready, and the knowledge about the standards and specifications was clear and fresh.

## Future

By this point, it's already clear that **FastAPI** with its ideas is being useful for many people.

   * exception.
   *
   * @throws IllegalStateException when the call has already been executed.
   */
  fun enqueue(responseCallback: Callback)

  /** Cancels the request, if possible. Requests that are already complete cannot be canceled. */
  fun cancel()

  /**
   * Returns true if this call has been either [executed][execute] or [enqueued][enqueue]. It is an

      "Cannot call source()/target() on a EndpointPair from an undirected graph. Consider calling "
          + "adjacentNode(node) if you already have a node, or nodeU()/nodeV() if you don't.";
  static final String EDGE_ALREADY_EXISTS = "Edge %s already exists in the graph.";
  static final String ENDPOINTS_MISMATCH =
      "Mismatch: endpoints' ordering is not compatible with directionality of the graph";

      this.mutableValueGraph =
          graphBuilder.copy().incidentEdgeOrder(ElementOrder.<N>stable()).build();
    }

    /**
     * Adds {@code node} if it is not already present.
     *
     * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
     *
     * @return this {@code Builder} object
     */
    @CanIgnoreReturnValue