Navigation Controller Error - swift

Question

I have a navigation controller and I want the title to have a custom font. I have tried to do this but when it runs I get Thread 1: EXC_BAD_INSTRUCTION (code=EXC_1386_INVOP.subcode=0x0)
Here is my code.
import UIKit
class PriceCheckSpreadsheetViewController: UIViewController {
#IBOutlet weak var SpreadsheetView: UIWebView!
#IBOutlet weak var Loading: UIActivityIndicatorView!
#IBOutlet weak var BackButton: UIBarButtonItem!
#IBOutlet weak var ForwardButton: UIBarButtonItem!
#IBOutlet weak var NaviBar: UINavigationItem!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
let url = "http://www.backpack.tf/pricelist/spreadsheet"
let requestURL = NSURL(string: url)
let request = NSURLRequest(URL: requestURL!)
SpreadsheetView.loadRequest(request)
self.navigationController?.navigationBar.titleTextAttributes = [ NSFontAttributeName: UIFont(name: "TF2Build", size: 12)!]
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func webViewDidStartLoad(_ : UIWebView) {
Loading.startAnimating()
NSLog("Loading")
}
func webViewDidFinishLoad(_ : UIWebView) {
Loading.stopAnimating()
NSLog("Done")
if SpreadsheetView.canGoBack {
BackButton.enabled = true
}
else {
BackButton.enabled = false
}
if SpreadsheetView.canGoForward {
ForwardButton.enabled = true
}
else {
ForwardButton.enabled = false
}
}
#IBAction func Reload(sender: AnyObject) {
SpreadsheetView.reload()
}
#IBAction func Back(sender: AnyObject) {
SpreadsheetView.goBack()
}
#IBAction func Forward(sender: AnyObject) {
SpreadsheetView.goForward()
}
}