title: xamarin app crashes because of xamforms.controls.calendar
body: <p>I just updated my MAC system and all packages in my Xamarin Project, now the App always crashes due to the following exception:
  <strong>Object reference not set to an instance of an object</strong>
    <strong>at XamForms.Controls.iOS.CalendarButtonRenderer.OnElementPropertyChanged (System.Object sender, System.ComponentModel.PropertyChangedEventArgs e) [0x0004a] in :0</strong> 
    at (wrapper delegate-invoke) .invoke_void_object_PropertyChangedEventArgs(object,System.ComponentModel.PropertyChangedEventArgs)
    at Xamarin.Forms.BindableObject.OnPropertyChanged (System.String propertyName) [0x00000] in D:\a\1\s\Xamarin.Forms.Core\BindableObject.cs:229 
    at Xamarin.Forms.Element.OnPropertyChanged (System.String propertyName) [0x00000] in D:\a\1\s\Xamarin.Forms.Core\Element.cs:350 
    at Xamarin.Forms.BindableObject.ClearValue (Xamarin.Forms.BindableProperty property, System.Boolean fromStyle, System.Boolean checkAccess) [0x000c6] in D:\a\1\s\Xamarin.Forms.Core\BindableObject.cs:96 
    at Xamarin.Forms.BindableObject.ClearValue (Xamarin.Forms.BindableProperty property) [0x00000] in D:\a\1\s\Xamarin.Forms.Core\BindableObject.cs:48 
    at Xamarin.Forms.Platform.iOS.VisualElementRenderer<code>1[TElement].Dispose (System.Boolean disposing) [0x0007d] in &lt;db18f72e3204406988680543da513ace&gt;:0 
    at Xamarin.Forms.Platform.iOS.ViewRenderer</code>2[TView,TNativeView].Dispose (System.Boolean disposing) [0x0005c] in :0 
    at Xamarin.Forms.Platform.iOS.ButtonRenderer.Dispose (System.Boolean disposing) [0x00064] in D:\a\1\s\Xamarin.Forms.Platform.iOS\Renderers\ButtonRenderer.cs:66 
    at Foundation.NSObject.Dispose () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.4.0.2/src/Xamarin.iOS/Foundation/NSObject2.cs:147 
    at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose (System.Boolean disposing) [0x0003f] in D:\a\1\s\Xamarin.Forms.Platform.iOS\VisualElementPackager.cs:71 
    at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose () [0x00000] in D:\a\1\s\Xamarin.Forms.Platform.iOS\VisualElementPackager.cs:39 
    at Xamarin.Forms.Platform.iOS.VisualElementRenderer<code>1[TElement].Dispose (System.Boolean disposing) [0x00058] in &lt;db18f72e3204406988680543da513ace&gt;:0 
    at Foundation.NSObject.Dispose () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.4.0.2/src/Xamarin.iOS/Foundation/NSObject2.cs:147 
    at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose (System.Boolean disposing) [0x0003f] in D:\a\1\s\Xamarin.Forms.Platform.iOS\VisualElementPackager.cs:71 
    at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose () [0x00000] in D:\a\1\s\Xamarin.Forms.Platform.iOS\VisualElementPackager.cs:39 
    at Xamarin.Forms.Platform.iOS.VisualElementRenderer</code>1[TElement].Dispose (System.Boolean disposing) [0x00058] in :0 
    at Foundation.NSObject.Dispose () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.4.0.2/src/Xamarin.iOS/Foundation/NSObject2.cs:147 
    at Xamarin.Forms.Platform.iOS.VisualElementPackager.OnChildRemoved (Xamarin.Forms.VisualElement view) [0x0003e] in D:\a\1\s\Xamarin.Forms.Platform.iOS\VisualElementPackager.cs:124 
    at Xamarin.Forms.Platform.iOS.VisualElementPackager.OnChildRemoved (System.Object sender, Xamarin.Forms.ElementEventArgs e) [0x0000f] in D:\a\1\s\Xamarin.Forms.Platform.iOS\VisualElementPackager.cs:161 
    at Xamarin.Forms.Element.OnChildRemoved (Xamarin.Forms.Element child) [0x00007] in D:\a\1\s\Xamarin.Forms.Core\Element.cs:334 
    at Xamarin.Forms.VisualElement.OnChildRemoved (Xamarin.Forms.Element child) [0x00000] in D:\a\1\s\Xamarin.Forms.Core\VisualElement.cs:750 
    at Xamarin.Forms.TemplatedView.OnChildRemoved (Xamarin.Forms.Element child) [0x00000] in D:\a\1\s\Xamarin.Forms.Core\TemplatedView.cs:92 
    at Xamarin.Forms.Layout.OnInternalRemoved (Xamarin.Forms.View view) [0x00012] in D:\a\1\s\Xamarin.Forms.Core\Layout.cs:473 
    at Xamarin.Forms.Layout.InternalChildrenOnCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x0002b] in D:\a\1\s\Xamarin.Forms.Core\Layout.cs:436 
    at System.Collections.ObjectModel.ObservableCollection<code>1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e) [0x00018] in &lt;429bba1022b24f41b20fdc67c7554c2d&gt;:0 
    at System.Collections.ObjectModel.ObservableCollection</code>1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedAction action, System.Object item, System.Int32 index) [0x00009] in &lt;429bba1022b24f41b20fdc67c7554c2d>:0 
    at System.Collections.ObjectModel.ObservableCollection<code>1[T].RemoveItem (System.Int32 index) [0x00021] in &lt;429bba1022b24f41b20fdc67c7554c2d&gt;:0 
    at System.Collections.ObjectModel.Collection</code>1[T].RemoveAt (System.Int32 index) [0x00027] in :0 
    at Xamarin.Forms.TemplateUtilities.OnContentChanged (Xamarin.Forms.BindableObject bindable, System.Object oldValue, System.Object newValue) [0x00018] in D:\a\1\s\Xamarin.Forms.Core\TemplateUtilities.cs:63 
    at Xamarin.Forms.BindableObject.SetValueActual (Xamarin.Forms.BindableProperty property, Xamarin.Forms.BindableObject+BindablePropertyContext context, System.Object value, System.Boolean currentlyApplying, Xamarin.Forms.Internals.SetValueFlags attributes, System.Boolean silent) [0x00120] in D:\a\1\s\Xamarin.Forms.Core\BindableObject.cs:463 
    at Xamarin.Forms.BindableObject.SetValueCore (Xamarin.Forms.BindableProperty property, System.Object value, Xamarin.Forms.Internals.SetValueFlags attributes, Xamarin.Forms.BindableObject+SetValuePrivateFlags privateAttributes) [0x00173] in D:\a\1\s\Xamarin.Forms.Core\BindableObject.cs:397 
    at Xamarin.Forms.BindableObject.SetValue (Xamarin.Forms.BindableProperty property, System.Object value, System.Boolean fromStyle, System.Boolean checkAccess) [0x00042] in D:\a\1\s\Xamarin.Forms.Core\BindableObject.cs:334 
    at Xamarin.Forms.BindableObject.SetValue (Xamarin.Forms.BindableProperty property, System.Object value) [0x00000] in D:\a\1\s\Xamarin.Forms.Core\BindableObject.cs:311 
    at Xamarin.Forms.ContentView.set_Content (Xamarin.Forms.View value) [0x00000] in D:\a\1\s\Xamarin.Forms.Core\ContentView.cs:11 
    <strong>at XamForms.Controls.Calendar+&lt;>c__DisplayClass89_0.b__0 () [0x00027] in &lt;78f786ab622940c1b06f4cfd4c30dce1>:0</strong> 
    at Foundation.NSAsyncActionDispatcher.Apply () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.4.0.2/src/Xamarin.iOS/Foundation/NSAction.cs:152 
    at (wrapper managed-to-native) UIKit.UIApplication.UIApplicationMain(int,string[],intptr,intptr)
    at UIKit.UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate) [0x00005] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.4.0.2/src/Xamarin.iOS/UIKit/UIApplication.cs:86 
    at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0000e] in /Library/Frameworks/Xamarin.iOS.framework/Versions/13.4.0.2/src/Xamarin.iOS/UIKit/UIApplication.cs:65 
    at myproject.iOS.Application.Main (System.String[] args) [0x00001] in /Users/lin/Projects/myProject/iOS/Main.cs:12 </p>