iterator: mergedIterator: Assert nil key
iterator: mergedIterator: Assert nil key

syndtr/goleveldb,chai2010/goleveldb,btcsuite/goleveldb,conseweb/goleveldb,FactomProject/goleveldb,zzl0/goleveldb,trigrass2/goleveldb,rentongzhang/goleveldb,no2key/goleveldb,hustbill/goleveldb,ngaut/goleveldb