code: public Logger defaultLogger() {
      if (this.defaultLogger != null) {
        return defaultLogger;
      }
  
      if (loggerProviderKeeper != null) {
        final LoggerProvider maybeLoggerProvider = loggerProviderKeeper.findDefault();
        this.defaultLogger = maybeLoggerProvider != null ?
            maybeLoggerProvider.logger() :
            LoggerProvider.noOpLoggerProvider().logger();
      }
  
      if (this.defaultLogger == null) {
        this.defaultLogger = LoggerProvider.standardLoggerProvider(this, "vlingo").logger();
      }
  
      return this.defaultLogger;
    }
docs: Answers the default {@code Logger} that is registered with this {@code World}. The
  {@code Logger} protocol is implemented by an {@code Actor} such that all logging is
  asynchronous.
  @return Logger