* delegating calls until it returns valid data.
   *
   * <p>If {@code delegate} is an instance created by an earlier call to {@code memoize}, it is
   * returned directly.
   */
  public static <T extends @Nullable Object> Supplier<T> memoize(Supplier<T> delegate) {
    if (delegate instanceof NonSerializableMemoizingSupplier
        || delegate instanceof MemoizingSupplier) {
      return delegate;
    }

   * delegating calls until it returns valid data.
   *
   * <p>If {@code delegate} is an instance created by an earlier call to {@code memoize}, it is
   * returned directly.
   */
  public static <T extends @Nullable Object> Supplier<T> memoize(Supplier<T> delegate) {
    if (delegate instanceof NonSerializableMemoizingSupplier
        || delegate instanceof MemoizingSupplier) {
      return delegate;
    }