fatal error: unexpectedly found nil while unwrapping an Optional value

[datomnurdin]

I'm doing bridging header but it throw an error message

fatal error: unexpectedly found nil while unwrapping an Optional value

My code

@IBAction func btnLinkedin(sender: AnyObject) {
if btnLinkedin.on {
client.getAuthorizationCode({ (code:String!) -> Void in
println(code)
self.client.getAccessToken(code, success: { (accessTokenData) -> Void in
if let dict = accessTokenData as? Dictionary<String, AnyObject> {
let accessToken: AnyObject? = dict["access_token"]
self.requestMeWithToken(accessToken!)
}
}, failure: { (error:NSError!) -> Void in
println("Quering accessToken failed (error)")
})
}, cancel: { () -> Void in
println("Authorization was cancelled by user")
}, failure: { (error:NSError!) -> Void in
println("Authorization failed (error)")
})
println("Switch is on")
btnLinkedin.setOn(true, animated:true)
} else {
println("Switch is off")
btnLinkedin.setOn(false, animated:true)
}
}

func requestMeWithToken(accessToken: AnyObject){
    client.GET("https://api.linkedin.com/v1/people/~?oauth2_access_token=%@&format=json", parameters: nil, success: { (operation:AFHTTPRequestOperation!, result:AnyObject!) -> Void in
        println("current user \(result)")
        }) { (operation: AFHTTPRequestOperation!, error:NSError!) -> Void in
        println("failed to fetch current user \(error)")
    }
}

Please advice.