@Nullable
    private static String serializationFormat(RequestLog requestLog) {
        final SerializationFormat serFmt = requestLog.serializationFormat();
        return serFmt == SerializationFormat.NONE ? null : serFmt.uriText();
    }
Returns the {@link SerializationFormat#uriText()} if it's not {@link SerializationFormat#NONE}.
core/src/main/java/com/linecorp/armeria/server/observation/DefaultServiceObservationConvention.java