title: Issue with retrieving Double number from Firebase Swift
body: <p>I am currently working on restaurants' project where from by pressing a button on Restaurant View controller I am viewing the location of the restaurant on google map (map view controller). In order to place latitude and longitude in my map code, I have an issue with retrieving Double numbers from Firebase. Whenever I try to print them, I get this error "fatal error: unexpectedly found nil while unwrapping an Optional value (lldb)" </p>
  
  <pre><code>GMSServices.provideAPIKey("AIzaSyRQKeLyKH5CsrDPpPsjy7nYqudEbqXmQS2")
          let ref = Database.database().reference().child("amsterdam")
          ref.queryOrdered(byChild: "name").queryEqual(toValue: self.appDelegate.selectedBarName).observe(.value) { (snapshot) in
              for child in snapshot.children{
                  let snap = child as! DataSnapshot
                  let mapSnap = snap.childSnapshot(forPath: "map")
                  if let snapDict = mapSnap.value as? [String:AnyObject]{
                      let dictValues = [AnyObject](snapDict.values)
                      for each in dictValues{
                          let latitude = each["map_latitude"] as! Double
                          let longitude = each["map_longitude"] as! Double
  
                          print(latitude)
                          print(longitude)
                         let camera = GMSCameraPosition.camera(withLatitude: latitude, longitude: longitude, zoom: 6.0)
                          let mapView = GMSMapView.map(withFrame: CGRect.zero, camera: camera)
                          self.view = mapView
                          let marker = GMSMarker()
                          marker.position = CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
                          marker.map = mapView
                      }
              }
          }
      }
  }
  </code></pre>