docs: public static <T1, T2> FluentFunctions.FluentBiFunction<T1, T2, Tuple2<T1, T2>> expression(final BiConsumer<? super T1, ? super T2> action) {
          return FluentFunctions.of((t1, t2) -> {
              action.accept(t1, t2);
              return Tuple.tuple(t1, t2);
          });
      }