title: Simply throw exception with message in swift 2.1
body: <p>I am simply looking something up in the plist. If there was some sort of error. How do you just say Exception("Missing Information")</p>
  
  <pre><code>class func Lookup() throws -&gt; String{
      let defaults = NSUserDefaults.standardUserDefaults()
      if let url = defaults.objectForKey("url"){
  
          return url as! String
      }
      if let path = NSBundle.mainBundle().pathForResource("Info", ofType: "plist"), dictionary = NSDictionary(contentsOfFile: path) as? [String: AnyObject] {
          if let url = dictionary["url"] {
              defaults.setValue(api, forKey: "url")
              defaults.synchronize()
              return url as! String
          }
      }
      return Exception("missing data") //something like this
  }
  </code></pre>