Custom pin image in annotationView in iOS

I'm trying to change from Swift 1.2 to Swift 2.0 and I'm at the end of the changes. Currently I'm making changes in the MapViewController, and there isn't any error or warning, but the custom image for my pin (annotationView) it's not assigned to the pin and it's showing the default one (red dot).

Here is my code, I hope you can help me with some tip because I think everything is fine but it's still not working:

func parseJsonData(data: NSData) -> [Farmacia] {

    let farmacias = [Farmacia]()

    do
    {
        let jsonResult = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers) as? NSDictionary

        // Parse JSON data
        let jsonProductos = jsonResult?["farmacias"] as! [AnyObject]

        for jsonProducto in jsonProductos {

            let farmacia = Farmacia()
            farmacia.id = jsonProducto["id"] as! String
            farmacia.nombre = jsonProducto["nombre"] as! String
            farmacia.location = jsonProducto["location"] as! String

            let geoCoder = CLGeocoder()
            geoCoder.geocodeAddressString(farmacia.location, completionHandler: { placemarks, error in

                if error != nil {
                    print(error)
                    return
                }

                if placemarks != nil && placemarks!.count > 0 {

                    let placemark = placemarks?[0]

                    // Add Annotation
                    let annotation = MKPointAnnotation()
                    annotation.title = farmacia.nombre
                    annotation.subtitle = farmacia.id
                    annotation.coordinate = placemark!.location!.coordinate

                    self.mapView.addAnnotation(annotation)
                }

            })
        }
    }
    catch let parseError {
        print(parseError)
    }

    return farmacias
}

func mapView(mapView: MKMapView, viewForAnnotation annotation: MKAnnotation) -> MKAnnotationView? {

    let identifier = "MyPin"

    if annotation.isKindOfClass(MKUserLocation) {
        return nil
    }

    // Reuse the annotation if possible
    var annotationView = mapView.dequeueReusableAnnotationViewWithIdentifier(identifier)

    if annotationView == nil
    {
        annotationView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: identifier)
        annotationView!.canShowCallout = true
    }

    annotationView!.image = UIImage(named: "custom_pin.png")

    let detailButton: UIButton = UIButton(type: UIButtonType.DetailDisclosure)
    annotationView!.rightCalloutAccessoryView = detailButton

    print(annotationView!.image)

    return annotationView
}

Thanks in advance,

Regards.

The accepted answer doesn't work, as it has annotationView uninitialized in else block.

Here's a better solution. It dequeues annotation view if possible or creates a new one if not:

// https://stackoverflow.com/a/38159048/1321917
func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
    // Don't want to show a custom image if the annotation is the user's location.
    guard !(annotation is MKUserLocation) else {
        return nil
    }

    // Better to make this class property
    let annotationIdentifier = "AnnotationIdentifier"

    var annotationView: MKAnnotationView?
    if let dequeuedAnnotationView = mapView.dequeueReusableAnnotationView(withIdentifier: annotationIdentifier) {
        annotationView = dequeuedAnnotationView
        annotationView?.annotation = annotation
    }
    else {
        annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: annotationIdentifier)
        annotationView?.rightCalloutAccessoryView = UIButton(type: .detailDisclosure)
    }

    if let annotationView = annotationView {
        // Configure your annotation view here
        annotationView.canShowCallout = true
        annotationView.image = UIImage(named: "yourImage")
    }

    return annotationView
}