Crash : AES128 encryption in iOS 10 using Swift 2.1 -

i’m using aes128 encryption. below code i’ve used :

. . . let encjson : string = response.objectforkey("data") as! string  let encryptionkey : string = “some key here”  //crash on line response = encryptionandconversion.sharedinstance.converencdatatostringwithaes128(encjson, key: encryptionkey)  print("response : \(response)") . . .  func converencdatatostringwithaes128(message:string, key mykey:string) -> nsdictionary {          let data = nsdata(base64encodedstring: message, options: nsdatabase64decodingoptions(rawvalue: 0))          //the value of result comes nil         let result = nsstring(data: (data?.aes128decrypteddatawithkey(mykey))!, encoding: nsutf8stringencoding)          return convertstringtodictionary(result!)     } 

what might reason? i’m getting crash on converencdatatostringwithaes128(..) function reason fatal error: unexpectedly found nil while unwrapping optional value

i’ve cross-verified there no issue message , key.

any appreciated!

not answer, crashes?

let encjson : string = response.objectforkey("data") as! string 

to:

guard let encjson = response.objectforkey("data") as? string {     print("data not string")     return }