title: NSInvalidArgumentException when trying to call annotations
body: <p>Annotations are displayed fine on the map, but when i click on one, i git this exception:</p>
  
  <pre><code>[NSNull length]: unrecognized selector sent to instance
  'NSInvalidArgumentException', reason: '-[NSNull length]: unrecognized selector sent to instance 
  </code></pre>
  
  <p>My relevant code is this:</p>
  
  <pre><code>- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id &lt;MKAnnotation&gt;)annotation {
  
      static NSString *identifier = @"MyLocation";   
      if ([annotation isKindOfClass:[MyLocation class]]) {
  
          MKPinAnnotationView *annotationView = (MKPinAnnotationView *) [mapView2 dequeueReusableAnnotationViewWithIdentifier:identifier];
          if (annotationView == nil) {
              annotationView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:identifier];
          } else {
              annotationView.annotation = annotation;
          }
  
          annotationView.enabled = YES;
          annotationView.canShowCallout = YES;
  
          annotationView.pinColor = MKPinAnnotationColorRed;
          return annotationView;
      }
  
      return nil;    
  }
  </code></pre>
  
  <p>And to configure the annotations:</p>
  
  <pre><code>NSNumber * latitude = [[row objectAtIndex:21]objectAtIndex:1];
          NSNumber * longitude = [[row objectAtIndex:21]objectAtIndex:2];
          NSString * crimeDescription = [row objectAtIndex:17];
          NSString * address = [row objectAtIndex:13];
  
          CLLocationCoordinate2D coordinate;
          coordinate.latitude = latitude.doubleValue;
          coordinate.longitude = longitude.doubleValue;            
          MyLocation *annotation = [[MyLocation alloc] initWithName:crimeDescription address:address coordinate:coordinate] ;
          [mapView2 addAnnotation:annotation];
  </code></pre>
  
  <p>And in <code>MyLocation</code> class which holds the annotations:</p>
  
  <pre><code>- (id)initWithName:(NSString*)name address:(NSString*)address coordinate:(CLLocationCoordinate2D)coordinate {
      if ((self = [super init])) {
          _name = [name copy];
          _address = [address copy];
          _coordinate = coordinate;
      }
      return self;
  }
  </code></pre>