private abstract static class RawTypeConsistencyTester<T extends Enum<T> & CharSequence> {
    abstract T returningT();

    abstract void acceptT(T t);

    abstract <X extends T> X returningX();

    abstract <X> void acceptX(X x);

    abstract <T2 extends Enum<T2> & CharSequence> T2 returningT2();

    abstract <T2 extends CharSequence & Iterable<T2>> void acceptT2(T2 t2);

  private abstract static class RawTypeConsistencyTester<T extends Enum<T> & CharSequence> {
    abstract T returningT();

    abstract void acceptT(T t);

    abstract <X extends T> X returningX();

    abstract <X> void acceptX(X x);

    abstract <T2 extends Enum<T2> & CharSequence> T2 returningT2();

    abstract <T2 extends CharSequence & Iterable<T2>> void acceptT2(T2 t2);

                "Method com.example.Source.baz(): From non-null returning to null-unmarked returning breaking change.",
            )
            assertHasNoWarning()
            assertHasNoInformation()
        }
    }

    @Test
    fun `from null-unmarked returning to non-null returning is not breaking`() {

    results.add(serializer.submit(Callables.returning(null), manualExecutor));
    Future<?>[] thingToCancel = new Future<?>[1];
    results.add(
        serializer.submit(
            () -> {
              thingToCancel[0].cancel(false);
              return null;
            },
            directExecutor()));
    thingToCancel[0] = serializer.submit(Callables.returning(null), directExecutor());

In this example, the function `generate_html_response()` already generates and returns a `Response` instead of returning the HTML in a `str`.

By returning the result of calling `generate_html_response()`, you are already returning a `Response` that will override the default **FastAPI** behavior.

FastAPI will use this return type to:

* **Validate** the returned data.
    * If the data is invalid (e.g. you are missing a field), it means that *your* app code is broken, not returning what it should, and it will return a server error instead of returning incorrect data. This way you and your clients can be certain that they will receive the data and the data shape expected.
* Add a **JSON Schema** for the response, in the OpenAPI *path operation*.

You can also use it directly to create an instance of it and return it from your *path operations*.

Read more about it in the [FastAPI docs about returning a custom Response](https://fastapi.tiangolo.com/advanced/response-directly/#returning-a-custom-response)

You can import it directly from `fastapi`:

```python
from fastapi import Response
```

    results.add(serializer.submit(Callables.returning(null), manualExecutor));
    Future<?>[] thingToCancel = new Future<?>[1];
    results.add(
        serializer.submit(
            () -> {
              thingToCancel[0].cancel(false);
              return null;
            },
            directExecutor()));
    thingToCancel[0] = serializer.submit(Callables.returning(null), directExecutor());

                errors << "From non-null returning to null returning breaking change"
            } else if (oldNullability == Nullability.NON_NULL && newNullability == Nullability.UNMARKED) {
                errors << "From non-null returning to null-unmarked returning breaking change"
            } else if (oldNullability == Nullability.UNMARKED && newNullability == Nullability.NULLABLE) {

    assertFalse(task.isDone());
    task.run();
    assertTrue(task.isDone());
    assertFalse(task.isCancelled());
    assertEquals(2, getDone(task).intValue());
  }

  public void testCancelled() throws Exception {
    TrustedListenableFutureTask<Integer> task = TrustedListenableFutureTask.create(returning(2));
    assertFalse(task.isDone());
    task.cancel(false);