SFSafariViewController crash: The specified URL has an unsupported scheme.

My code:

if let url = NSURL(string: "www.google.com") {
    let safariViewController = SFSafariViewController(URL: url)
    safariViewController.view.tintColor = UIColor.wantoPrimaryOrangeColor()
    presentViewController(safariViewController, animated: true, completion: nil)
}

This crashes on initialization only with exception:

The specified URL has an unsupported scheme. Only HTTP and HTTPS URLs are supported

When I use url = NSURL(string: "http://www.google.com"), everything is fine. I am actually loading URL's from API and hence, I can't be sure that they will be prefixed with http(s)://.

How to tackle this problem? Should I check and prefix http:// always, or there's a workaround?