code: @SuppressWarnings("rawtypes")
    public static <R> Fallback<R> of(R fallback) {
      return new Fallback<>(Functions.fnOf(Assert.notNull(fallback, "fallback")), false);
    }
docs: Configures the {@code fallback} result to be returned if execution fails.
  
  @throws NullPointerException if {@code fallback} is null