NullReferenceException throws on Windows when setting Cookies on .NET MAUI WebView

src/Controls/tests/TestCases.HostApp/Issues/Issue18452.cs

@@ -0,0 +1,59 @@
+using System.Net;
+
+namespace Maui.Controls.Sample.Issues
+{
+	[Issue(IssueTracker.Github, 18452, "NullReferenceException throws on Windows when setting Cookies on .NET MAUI WebView", PlatformAffected.UWP)]
+	public class Issue18452 : TestContentPage
+	{
+		protected override void Init()
+		{
+			Grid grid = new Grid();
+			grid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(0.8, GridUnitType.Star) });
+			grid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(0.2, GridUnitType.Star) });
+			WebView webView = new WebView();
+
+			Label label = new Label();
+			label.AutomationId = "Label";
+
+			const string url = "https://learn.microsoft.com/en-us/dotnet/";
+
+			CookieContainer cookieContainer = new();
+			Uri uri = new(url, UriKind.RelativeOrAbsolute);
+
+			Cookie cookie = new()
+			{
+				Name = "DotNetMAUICookie",
+				Expires = DateTime.Now.AddDays(1),
+				Value = "My cookie",
+				Domain = uri.Host,
+				Path = "/"
+			};
+
+			cookieContainer.Add(uri, cookie);
+			webView.Cookies = cookieContainer;
+			webView.AutomationId = "WebView";
+			webView.Source = new UrlWebViewSource { Url = uri.ToString() };
+
+			grid.Children.Add(webView);
+
+			webView.Navigated += (s, e) =>
+			{
+				var cookies = webView.Cookies.GetCookies(uri);
+				foreach (Cookie c in cookies)
+				{
+					if (c.Name == "DotNetMAUICookie")
+					{
+						if (!grid.Contains(label))
+                        {
+                            grid.Children.Add(label);
+                            label.Text = "Success";
+                            break;
+                        }
+					}
+				}
+			};
+
+			Content = grid;
+		}
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue18452.cs

@@ -0,0 +1,24 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+[Category(UITestCategories.WebView)]
+public class Issue18452 : _IssuesUITest
+{
+	public override string Issue => "NullReferenceException throws on Windows when setting Cookies on .NET MAUI WebView";
+	string? expected = "Success";
+
+	public Issue18452(TestDevice device) : base(device)
+	{
+	}
+
+	[Test]
+	public void WebViewLoadedWithoutException()
+	{
+		App.WaitForElement("Label");
+		string? label = App.FindElement("Label").GetText();
+		Assert.That(label, Is.EqualTo(expected));
+	}
+}

src/Core/src/Handlers/WebView/WebViewHandler.Windows.cs

@@ -207,6 +207,11 @@ internal async Task SyncPlatformCookies(string url)
 			if (myCookieJar is null)
 				return;
 
+			if (PlatformView.CoreWebView2 is null)
+			{
+				return;
+			}
+
 			await InitialCookiePreloadIfNecessary(url);
 			var cookies = myCookieJar.GetCookies(uri);
 
@@ -366,6 +371,10 @@ void OnCoreWebView2Initialized(WebView2 sender, CoreWebView2InitializedEventArgs
 				if (Handler is WebViewHandler handler)
 				{
 					sender.UpdateUserAgent(handler.VirtualView);
+				    if (sender.Source is not null)
+					{
+						handler.SyncPlatformCookies(sender.Source.ToString()).FireAndForget();
+					}
 				}
 			}
 
@@ -405,4 +414,4 @@ void OnProcessFailed(CoreWebView2 sender, CoreWebView2ProcessFailedEventArgs arg
 			}
 		}
 	}
-}
+}