Fix exception when switching to invalid NuGet package source url.

src/AddIns/Misc/PackageManagement/Project/Src/AvailablePackagesViewModel.cs

@@ -68,6 +68,7 @@ namespace ICSharpCode.PackageManagement
 			try {
 				repository = RegisteredPackageRepositories.ActiveRepository;
 			} catch (Exception ex) {
+				repository = null;
 				errorMessage = ex.Message;
 			}
 		}

src/AddIns/Misc/PackageManagement/Test/Src/AvailablePackagesViewModelTests.cs

@@ -385,7 +385,7 @@ namespace PackageManagement.Tests
 		public void ReadPackages_ExceptionThrownWhenAccessingActiveRepository_ErrorMessageFromExceptionNotOverriddenByReadPackagesCall()
 		{
 			CreateExceptionThrowingRegisteredPackageRepositories();
-			exceptionThrowingRegisteredPackageRepositories.ExeptionToThrowWhenActiveRepositoryAccessed = 
+			exceptionThrowingRegisteredPackageRepositories.ExceptionToThrowWhenActiveRepositoryAccessed = 
 				new Exception("Test");
 			CreateViewModel(exceptionThrowingRegisteredPackageRepositories);
 			viewModel.ReadPackages();
@@ -621,5 +621,33 @@ namespace PackageManagement.Tests
 			};
 			PackageCollectionAssert.AreEqual(expectedPackages, allPackages);
 		}
+		
+		[Test]
+		public void ReadPackages_ActiveRepositoryChangedWhichUsesInvalidUrl_InvalidUrlExceptionIsShownAsErrorMessage()
+		{
+			CreateExceptionThrowingRegisteredPackageRepositories();
+			CreateViewModel(exceptionThrowingRegisteredPackageRepositories);
+			var package = new FakePackage("Test", "0.1.0.0");
+			exceptionThrowingRegisteredPackageRepositories
+				.FakeActiveRepository
+				.FakePackages
+				.Add(package);
+			viewModel.ReadPackages();
+			CompleteReadPackagesTask();
+			taskFactory.ClearAllFakeTasks();
+			exceptionThrowingRegisteredPackageRepositories.ExceptionToThrowWhenActiveRepositoryAccessed =
+				new Exception("Invalid url");
+			
+			viewModel.ReadPackages();
+			FakeTask<PackagesForSelectedPageResult> task = taskFactory.FirstFakeTaskCreated;
+			ApplicationException ex = Assert.Throws<ApplicationException>(() => task.ExecuteTaskButNotContinueWith());
+			task.Exception = new AggregateException(ex);
+			task.IsFaulted = true;
+			task.ExecuteContinueWith();
+			
+			Assert.AreEqual("Invalid url", ex.Message);
+			Assert.IsTrue(viewModel.HasError);
+			Assert.AreEqual("Invalid url", viewModel.ErrorMessage);
+		}
 	}
 }

src/AddIns/Misc/PackageManagement/Test/Src/Helpers/ExceptionThrowingRegisteredPackageRepositories.cs

@@ -25,23 +25,23 @@ namespace PackageManagement.Tests.Helpers
 {
 	public class ExceptionThrowingRegisteredPackageRepositories : FakeRegisteredPackageRepositories
 	{
-		public Exception ExeptionToThrowWhenActiveRepositoryAccessed { get; set; }
+		public Exception ExceptionToThrowWhenActiveRepositoryAccessed { get; set; }
 		
 		public override IPackageRepository ActiveRepository {
 			get {
-				if (ExeptionToThrowWhenActiveRepositoryAccessed != null) {
-					throw ExeptionToThrowWhenActiveRepositoryAccessed;
+				if (ExceptionToThrowWhenActiveRepositoryAccessed != null) {
+					throw ExceptionToThrowWhenActiveRepositoryAccessed;
 				}
 				return base.ActiveRepository;
 			}
 		}
 		
-		public Exception ExeptionToThrowWhenRecentPackageRepositoryAccessed { get; set; }
+		public Exception ExceptionToThrowWhenRecentPackageRepositoryAccessed { get; set; }
 		
 		public override IRecentPackageRepository RecentPackageRepository {
 			get {
-				if (ExeptionToThrowWhenRecentPackageRepositoryAccessed != null) {
-					throw ExeptionToThrowWhenRecentPackageRepositoryAccessed;
+				if (ExceptionToThrowWhenRecentPackageRepositoryAccessed != null) {
+					throw ExceptionToThrowWhenRecentPackageRepositoryAccessed;
 				}
 				return base.RecentPackageRepository;
 			}

src/AddIns/Misc/PackageManagement/Test/Src/RecentPackagesViewModelTests.cs

@@ -143,7 +143,7 @@ namespace PackageManagement.Tests
 		public void ReadPackages_ExceptionThrownWhenAccessingActiveRepository_ErrorMessageFromExceptionNotOverriddenByReadPackagesCall()
 		{
 			var registeredRepositories = new ExceptionThrowingRegisteredPackageRepositories();
-			registeredRepositories.ExeptionToThrowWhenRecentPackageRepositoryAccessed = 
+			registeredRepositories.ExceptionToThrowWhenRecentPackageRepositoryAccessed = 
 				new Exception("Test");
 			CreateViewModel(registeredRepositories);