bugfix: reduce with empty seq
bugfix: reduce with empty seq

oceanjack/dpark,windreamer/dpark,smarthomekit/dpark,yhj630520/dpark,junmoa/dpark,douban/dpark,smarthomekit/dpark,mageia/dpark,dogeyes/dpark,dogeyes/dpark,veritynoob/dpark,windreamer/dpark,yanheven/dpark,quxiaolong1504/dpark,daishaowei/dpark,mageia/dpark,junmoa/dpark,304471720/dpark,douban/dpark,daishaowei/dpark,yanheven/dpark,fe11x/dpark,Mignet/dpark,dogeyes/dpark,yhj630520/dpark,smarthomekit/dpark,zzl0/dpark,Mignet/dpark,yhj630520/dpark,quxiaolong1504/dpark,veritynoob/dpark,fe11x/dpark,windreamer/dpark,304471720/dpark,ee08b397/dpark,douban/dpark,veritynoob/dpark,zzl0/dpark,windreamer/dpark,304471720/dpark,oceanjack/dpark,douban/dpark,douban/dpark