code: public <B> MonoT<W,B> flatMapT(final Function<? super T, MonoT<W,B>> f) {
          MonoT<W, B> r = of(run.map(future -> Mono.from(future.flatMap(a -> {
              Mono<B> m = f.apply(a).run.stream()
                      .toList()
                      .get(0);
              return m;
          }))));
          return r;
      }
docs: Flat Map the wrapped Mono
  
  @param f FlatMap function
  @return MonoT that applies the flatMap function to the wrapped Mono