title: Nil is incompatible with return type 'MKOverlayRenderer'
body: <p>I am getting this error</p>
  
  <blockquote>
    <p><strong>"Nil is incompatible with return type 'MKOverlayRenderer'"</strong>.</p>
  </blockquote>
  
  <p>Here is my code:</p>
  
  <pre><code>func mapView(mapView: MKMapView, rendererForOverlay overlay: MKOverlay) -&gt; MKOverlayRenderer {
      if overlay is MKCircle {
        let circleRenderer = MKCircleRenderer(overlay: overlay)
        circleRenderer.lineWidth = 1.0
        circleRenderer.strokeColor = UIColor.purpleColor()
        circleRenderer.fillColor = UIColor.purpleColor().colorWithAlphaComponent(0.4)
        return circleRenderer
      }
        return nil
    }
  </code></pre>
  
  <p>why is it occurring?</p>