code: public final Mono<T> log(@Nullable String category) {
  		return log(category, Level.INFO);
  	}
docs: Observe all Reactive Streams signals and use {@link Logger} support to handle trace implementation. Default will
  use {@link Level#INFO} and java.util.logging. If SLF4J is available, it will be used instead.
  
  <p>
  <img class="marble" src="doc-files/marbles/logForMono.svg" alt="">
  
  @param category to be mapped into logger configuration (e.g. org.springframework
  .reactor). If category ends with "." like "reactor.", a generated operator
  suffix will complete, e.g. "reactor.Flux.Map".
  
  @return a new {@link Mono}