docs: public <T1> Mutable<T1> mapInputToObj(final Function<T1, Boolean> fn) {
          final MutableBoolean host = this;
          return new Mutable<T1>() {
              @Override
              public Mutable<T1> set(final T1 value) {
                  host.set(fn.apply(value));
                  return this;
              }
  
          };
      }