gistfile1.txt

System.NullReferenceException: Object reference not set to an instance of an object
  at MapCallouts.MainViewController.GetViewForAnnotation (MonoTouch.MapKit.MKMapView mapView, MonoTouch.Foundation.NSObject annotation) [0x000ce] in /Users/nischal/Desktop/monotouch-samples-master/MapCallouts/MainViewController.cs:149
  at MonoTouch.MapKit.MKMapView+_MKMapViewDelegate.GetViewForAnnotation (MonoTouch.MapKit.MKMapView mapView, MonoTouch.Foundation.NSObject annotation) [0x0000d] in /Developer/MonoTouch/Source/monotouch/src/MapKit/MKMapView.g.cs:1120
  at at (wrapper managed-to-native) MonoTouch.ObjCRuntime.Messaging:void_objc_msgSend_IntPtr (intptr,intptr,intptr)
  at MonoTouch.MapKit.MKMapView.AddAnnotationObject (MonoTouch.Foundation.NSObject annotation) [0x00021] in /Developer/MonoTouch/Source/monotouch/src/MapKit/MKMapView.g.cs:312
  at MonoTouch.MapKit.MKMapView.AddAnnotation (MonoTouch.MapKit.MKAnnotation annotation) [0x00000] in /Developer/MonoTouch/Source/monotouch/src/MapKit/MKMapView.cs:19
  at MapCallouts.MainViewController.cityAction (MonoTouch.Foundation.NSObject sender) [0x0000c] in /Users/nischal/Desktop/monotouch-samples-master/MapCallouts/MainViewController.cs:100
  at at (wrapper managed-to-native) MonoTouch.UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr)
  at MonoTouch.UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0004c] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIApplication.cs:38
  at MapCallouts.Application.Main (System.String[] args) [0x00000] in /Users/nischal/Desktop/monotouch-samples-master/MapCallouts/Main.cs:16