遍历table明细是否为空

//循环遍历 <tbody id="linedata2">,获取每行值对比
$("#linedata2 tr").each(function(i,n){
    var mappingProjectCode = $("mappingProjectCode",this).val();
    if(mappingProjectCode == null || mappingProjectCode == ''){
        must+="第("+(i+1)+")行xxx不能为空! ";
        errorFlag=true;
    }
});