code: public static TaggedLogger tag(final String tag) {
  		if (tag == null || tag.isEmpty()) {
  			return instance;
  		} else {
  			TaggedLogger logger = loggers.get(tag);
  			if (logger == null) {
  				logger = new TaggedLogger(tag);
  				TaggedLogger existing = loggers.putIfAbsent(tag, logger);
  				return existing == null ? logger : existing;
  			} else {
  				return logger;
  			}
  		}
  	}
docs: Gets a tagged logger instance. Tags are case-sensitive.
  
  @param tag
  Tag for logger or {@code null} for receiving an untagged logger
  @return Logger instance