code: public final Mono<T> next() {
  		if(this instanceof Callable){
  			@SuppressWarnings("unchecked")
  			Callable<T> m = (Callable<T>)this;
  			return convertToMono(m);
  		}
  		return Mono.onAssembly(new MonoNext<>(this));
  	}
docs: Emit only the first item emitted by this {@link Flux}, into a new {@link Mono}.
  <p>
  <img class="marble" src="doc-files/marbles/next.svg" alt="">
  
  @return a new {@link Mono} emitting the first value in this {@link Flux}