@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;
    }
    return new ImmediateFuture<>(value);
  }

  /**

      @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;
    }
    return new ImmediateFuture<>(value);
  }

  /**

      checkNotNull(
          replacement,
          "AsyncFunction.apply returned null instead of a Future. "
              + "Did you mean to return immediateFuture(null)? %s",
          fallback);
      return replacement;
    }

    @Override
    void setResult(ListenableFuture<? extends V> result) {
      setFuture(result);
    }
  }

  /**

      checkNotNull(
          outputFuture,
          "AsyncFunction.apply returned null instead of a Future. "
              + "Did you mean to return immediateFuture(null)? %s",
          function);
      return outputFuture;
    }

    @Override
    void setResult(ListenableFuture<? extends O> result) {
      setFuture(result);
    }
  }

  /**