}

    @SuppressWarnings("unchecked") // proxy for a generic class
    <V1, V2, V3, V4, U> ClosingFunction4<V1, V2, V3, V4, U> waitFor(
        ClosingFunction4<V1, V2, V3, V4, U> closingFunction4) {
      return waitFor(closingFunction4, ClosingFunction4.class);
    }

    @SuppressWarnings("unchecked") // proxy for a generic class

     * @param <V3> the type returned by the third future
     * @param <V4> the type returned by the fourth future
     * @param <U> the type returned by the function
     */
    public interface ClosingFunction4<
        V1 extends @Nullable Object,
        V2 extends @Nullable Object,
        V3 extends @Nullable Object,
        V4 extends @Nullable Object,
        U extends @Nullable Object> {
      /**

     * @param <V4> the type returned by the fourth future
     * @param <U> the type returned by the function
     */
    @FunctionalInterface
    public interface ClosingFunction4<
        V1 extends @Nullable Object,
        V2 extends @Nullable Object,
        V3 extends @Nullable Object,
        V4 extends @Nullable Object,
        U extends @Nullable Object> {
      /**