exc-bad-instruction code=i386_invop

I'm getting this error in latest version of xcode using swift 2

on line

let s = linkTxt.text

Text in linkTxt appears by button "pasteFromClipBoard"

let s = linkTxt.text
        let u = NSURL(string: s!)
        let file = u?.lastPathComponent

What is the reason of it and how to fix it?

Update:

the problem appears in function saveData() which calls when file downloading is finished. It calls from NSURLSessionDataTask function. More interesting, that in start-downloading-button there are the same lines where filename is generating and there is no such error on it. I fixed these issues by declaring variables, writing text's values into them and use these variables in saveData() except textObject.text; I had to delete lines with NSUserDefaults from saveData() too because I got the same error. Did understand nothing >_<

Update 2:

It's really a bug. I've deleted this line and wrote again - problem fixed

linkTxt.txt is returning nil and NSURL(string: s!) will try to forcefully unwrap it.

let s = linkTxt.text
if let s = linkTxt.txt {
    let u = NSURL(string: s!)
    let file = u?.lastPathComponent
}