Localization.IsLocalizationEnabled() not working within PageAsyncTask

[XHale84]

The AJAX Control Toolkit \18.1.1

The installation method

• NuGet package

Minimal steps to reproduce the bug

After migrating to AjaxControlToolkit 18.1.1 from 3.5 we are facing problems with AsyncTasks. We are loading Custom Controls (ascx) content within a AsyncTask via Page.RegisterAsyncTask().
But in this case we are getting a NullRefrenceExeption with the following StackTrace:

AjaxControlToolkit.Localization.IsLocalizationEnabled() bei
AjaxControlToolkit.Localization.GetLocaleKey() bei AjaxControlToolkit.Localization.RegisterLocalization(ClientScriptManager scriptManager, Type type) bei AjaxControlToolkit.ExtenderControlBase.OnPreRender(EventArgs e) bei System.Web.UI.Control.PreRenderRecursiveInternal() bei System.Web.UI.Control.PreRenderRecursiveInternal() bei System.Web.UI.Control.PreRenderRecursiveInternal() bei System.Web.UI.Control.PreRenderRecursiveInternal() bei
System.Web.UI.Control.AddedControl(Control control, Int32 index) bei System.Web.UI.ControlCollection.Add(Control child) bei System.Web.UI.WebControls.Repeater.CreateItem(Int32 itemIndex, ListItemType itemType, Boolean dataBind, Object dataItem) bei System.Web.UI.WebControls.Repeater.AddDataItemsIntoItemsArray(IEnumerable dataSource, Boolean useDataSource) bei
System.Web.UI.WebControls.Repeater.PostGetDataAction(IEnumerable dataSource) bei System.Web.UI.WebControls.Repeater.CreateControlHierarchy(Boolean useDataSource) bei System.Web.UI.WebControls.Repeater.OnDataBinding(EventArgs e) bei System.Web.UI.WebControls.Repeater.DataBind() bei
...
System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr md, Object[] args, Object server, Object[]& outArgs) bei System.Runtime.Remoting.Messaging.StackBuilderSink.AsyncProcessMessage(IMessage msg, IMessageSink replySink) Exception rethrown at [0]: bei System.Runtime.Remoting.Proxies.RealProxy.EndInvokeHelper(Message reqMsg, Boolean bProxyCase) bei System.Runtime.Remoting.Proxies.RemotingProxy.Invoke(Object NotUsed, MessageData& msgData) bei System.Action.EndInvoke(IAsyncResult result) bei
...

Actual result

NullReferenceException.
The problem is, that there is no HttpContext at this point, therefore the line
Page page = HttpContext.Current.Handler as Page;
will throw a NullReferenceException.

Expected result

The site should load as normal.

Browser(s) used

Chrome

A site deployment method

• IIS

[XHale84]

I think that could easily be fixed by replacing Localization.cs line 115 through this

var page = HttpContext.Current?.Handler as Page;