@Override
    public void start() {
        if (!aai.iteratorForAppenders().hasNext()) {
            addWarn("No appender was attached to " + getClass().getSimpleName() + '.');
        }
        super.start();
    }
Stores the specified {@link RequestContextExporterBuilder} customizer to be lazily applied when
the exporter is built.
logback/logback12/src/main/java/com/linecorp/armeria/common/logback/RequestContextExportingAppender.java