code: public boolean isLoggable(Level level) {
          if (level == null) {
              throw new NullPointerException();
          }
          // performance-sensitive method: use two monomorphic call-sites
          JavaLoggerProxy jlp = javaLoggerProxy;
          return jlp != null ? jlp.isLoggable(level) : loggerProxy.isLoggable(level);
      }
docs: Returns true if a message of the given level would actually
  be logged by this logger.