Firebase data and unexpected nil - swift

Question

My ultimate goal is to display annotations on a Map from MapKit. However, loading data from firebase does not work.
Here is the code:
var hotels = [Hotel]()
override func viewDidLoad() {
super.viewDidLoad()
map.delegate = self
checkLocationServices()
observe()
}
The function observe is the following:
func observe() {
Data().getAllHotel { (hotelA) -> (Void) in
if let hotel = hotelA {
print("hotel: ", hotel)
self.hotels.append(hotel)
let hotelAnnotation = MKPointAnnotation()
hotelAnnotation.title = "\(hotel.hotelName)"
hotelAnnotation.coordinate = CLLocationCoordinate2D(latitude: hotel.latitude, longitude: hotel.longitude)
self.map.addAnnotation(hotelAnnotation)
}
}
}
Note that the print in the if statement is not empty.
However the line hotelAnnotation.title causes a bug unexpected nil and I don't understand why.
Additionnally here is the getAllHotel function inside the Data class:
func getAllHotel(closure: HotelClosure?) {
let ref = Ref().databaseHotels
ref.observe(.childAdded) { (snapshot) in
if let dict = snapshot.value as? Dictionary<String, AnyObject> {
let hotel = self.fromDictToHotel(key: snapshot.key, dict: dict)
closure?(hotel)
} else {
closure?(nil)
}
}
}
func fromDictToHotel(key: String, dict: Dictionary<String, AnyObject>) -> Hotel? {
guard let hotelName = dict["name"] as? String else { return nil }
guard let latitude = dict["latitude"] as? Double else { return nil }
guard let longitude = dict["longitude"] as? Double else { return nil }
let hotelDescription = dict["description"] as? String
let hotelGrade = dict["grade"] as? Double
let hotelImageUrl = dict["hotelImageUrl"] as? String
let hotel = Hotel(hid: key, hotelName: hotelName, hotelDescription: hotelDescription, latitude: latitude, longitude: longitude, grade: hotelGrade, url: hotelImageUrl)
return hotel
}
Thanks in advance for your help!