Facebook Login with Swift crash issue

Since many times i did Objective-C coding but recently i am moving to swift. It look very new for for me. In My application i need to integrate Facebook while integrating i feel that Same code of block works nicely in Objective-C but in Swift it crashes inside Clouser while creating Facebook Session

See Attached image. It’s Headache now. Your help will be appreciate.

FBSession.activeSession().setStateChangeHandler({(currentSession:FBSession!, stateOfSession: FBSessionState!, sessionError: NSError!) in
        self.sessionStateChanged(currentSession, state: stateOfSession, error: sessionError)
    })