ios - exc-bad-instruction code=i386_invop -

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

on line

let s = linktxt.text 

text in linktxt appears button "pastefromclipboard"

let s = linktxt.text         let u = nsurl(string: s!)         let file = u?.lastpathcomponent 

what reason of , how fix it?

update:

the problem appears in function savedata() calls when file downloading finished. calls nsurlsessiondatatask function. more interesting, in start-downloading-button there same lines filename generating , there no such error on it. fixed these issues declaring variables, writing text's values them , use these variables in savedata() except textobject.text; had delete lines nsuserdefaults savedata() because got same error. did understand nothing >_<

update 2:

it's bug. i've deleted line , wrote again - problem fixed

linktxt.txt returning nil , nsurl(string: s!) try forcefully unwrap it.

let s = linktxt.text if let s = linktxt.txt {     let u = nsurl(string: s!)     let file = u?.lastpathcomponent }