public void mixIn(Class target, Class mixinSource) {
        if (mixinSource == null) {
            mixInCache.remove(target);
        } else {
            mixInCache.put(target, mixinSource);
        }
        cache.remove(target);
    }
@deprecated only use compatible with fastjson 1.x
core/src/main/java/com/alibaba/fastjson2/writer/ObjectWriterProvider.java