*
   * @since 8.0
   */
  public static <T extends @Nullable Object> Function<Supplier<T>, T> supplierFunction() {
    @SuppressWarnings("unchecked") // implementation is "fully variant"
    SupplierFunction<T> sf = (SupplierFunction<T>) SupplierFunctionImpl.INSTANCE;
    return sf;
  }

  private interface SupplierFunction<T extends @Nullable Object> extends Function<Supplier<T>, T> {}

   *
   * @since 8.0
   */
  public static <T extends @Nullable Object> Function<Supplier<T>, T> supplierFunction() {
    @SuppressWarnings("unchecked") // implementation is "fully variant"
    SupplierFunction<T> sf = (SupplierFunction<T>) SupplierFunctionImpl.INSTANCE;
    return sf;
  }

  private interface SupplierFunction<T extends @Nullable Object> extends Function<Supplier<T>, T> {}