add nil value filter for buildConditions
add nil value filter for buildConditions

ymhhh/xorm,Michael2008S/xorm,go-xorm/xorm,henrylee2cn/xorm,tempbottle/xorm,ymhhh/xorm,evalphobia/xorm,aviau/xorm,zj8487/xorm,toophy/xorm,zileyuan/xorm,vCaesar/xorm,lunny/xorm,henrylee2cn/xorm,tempbottle/xorm,zj8487/xorm,lunny/xorm,Michael2008S/xorm,go-xorm/xorm,toophy/xorm,zileyuan/xorm,aviau/xorm,vCaesar/xorm,evalphobia/xorm