private static Optional<AnnotationMirror> nullableIn(
      List<? extends AnnotationMirror> annotations) {
    return annotations.stream()
        .filter(a -> a.getAnnotationType().asElement().getSimpleName().contentEquals("Nullable"))
        .map(a -> (AnnotationMirror) a) // get rid of the pesky wildcard
        .findFirst();
  }
Returns a list that is either empty or contains a single element that is an appropriate
{@code @Nullable} type-annotation.
value/src/main/java/com/google/auto/value/processor/Nullables.java