mysql insert into怎么把空字符串转为NULL

$faceidResult = empty($faceidResult) ? "NULL" : "'$faceidResult'";
$sql = "INSERT INTO Cln_User (ID,Tel_Code, OtherImage, Ip_Country, Browser_Language, videoName, riskVideo,faceidResult, faceidStamp, riskStamp, Ip_City) 
　　　　　　　　VALUES (NULL,  '$Browser_Language', '$videoName', '$riskVideo', $faceidResult, '$faceidStamp', '$riskStamp', '$Ip_City');";