return new Assignability<>();
    }
  }

  private static void assertAssignable(TypeToken<?> from, TypeToken<?> to) {
    assertTrue(
        from.getType() + " is expected to be assignable to " + to.getType(),
        to.isSupertypeOf(from));
    assertTrue(
        to.getType() + " is expected to be a supertype of " + from.getType(),
        to.isSupertypeOf(from));
    assertTrue(

      return new Assignability<>();
    }
  }

  private static void assertAssignable(TypeToken<?> from, TypeToken<?> to) {
    assertTrue(
        from.getType() + " is expected to be assignable to " + to.getType(),
        to.isSupertypeOf(from));
    assertTrue(
        to.getType() + " is expected to be a supertype of " + from.getType(),
        to.isSupertypeOf(from));
    assertTrue(

   */
  public static <V extends @Nullable Object> ListenableFuture<V> immediateFuture(
      @ParametricNullness V value) {
    if (value == null) {
      // This cast is safe because null is assignable to V for all V (i.e. it is bivariant)
      @SuppressWarnings("unchecked")
      ListenableFuture<V> typedNull = (ListenableFuture<V>) ImmediateFuture.NULL;
      return typedNull;
    }