如果调用liststate.add（object-in），它只反序列化当前输入对象，而不是liststate中的所有元素

public void add(V value) {
    Preconditions.checkNotNull(value, "You cannot add null to a ListState.");

    try {
        this.writeCurrentKeyWithGroupAndNamespace();
        byte[] key = this.dataOutputView.getCopyOfBuffer();
        this.dataOutputView.clear();
        this.elementSerializer.serialize(value, this.dataOutputView);
        this.backend.db.merge(this.columnFamily, this.writeOptions, key, this.dataOutputView.getCopyOfBuffer());
    } catch (Exception var3) {
        throw new FlinkRuntimeException("Error while adding data to RocksDB", var3);
    }
}