ios – Unable to test Change circumstances with “null” worth in swift

To test a number of situations i’m utilizing change statements

code: right here all circumstances working high-quality however. right here if user_details?.ranking = "" is empty then i want to point out default case i imply all stars empty however its going to case _ the place user_details?.ranking ?? "" <= "1.9" why?

if i take advantage of case _ the place (user_details?.ranking)! <= "1.9": then app getting crash when attain this

if user_details?.ranking = “” then how one can present all stars empty please information me

change user_details?.ranking{

case "1.0":

    star1.picture = UIImage(named: "star")

    star2.picture = UIImage(named: "staremp")
    star3.picture = UIImage(named: "staremp")
    star4.picture = UIImage(named: "staremp")
    star5.picture = UIImage(named: "staremp")
break
case _ the place user_details?.ranking ?? "" <= "1.9":

    star1.picture = UIImage(named: "star")
    star2.picture = UIImage(named: "star-half")

    star3.picture = UIImage(named: "staremp")
    star4.picture = UIImage(named: "staremp")
    star5.picture = UIImage(named: "staremp")
break

case "2.0":

    star1.picture = UIImage(named: "star")
    star2.picture = UIImage(named: "star")

    star3.picture = UIImage(named: "staremp")
    star4.picture = UIImage(named: "staremp")
    star5.picture = UIImage(named: "staremp")

 break

case _ the place user_details?.ranking ?? "" <= "2.9":

    star1.picture = UIImage(named: "star")
    star2.picture = UIImage(named: "star")
    star3.picture = UIImage(named: "star-half")

    star4.picture = UIImage(named: "staremp")
    star5.picture = UIImage(named: "staremp")
 break


default:
    star1.picture = UIImage(named: "staremp")
    star2.picture = UIImage(named: "staremp")
    star3.picture = UIImage(named: "staremp")
    star4.picture = UIImage(named: "staremp")
    star5.picture = UIImage(named: "staremp")

break

}