@Nullable
    protected final Logger logger() {
        if (logWriterBuilder != null) {
            return logWriterBuilder.logger();
        }
        return null;
    }
Returns the {@link Logger} the user specified to use,
or {@code null} if not set and a default logger should be used.
core/src/main/java/com/linecorp/armeria/common/logging/LoggingDecoratorBuilder.java