Merge pull request #2362 from github/fixes/null-view-model

Return a null view for a null view-model

Author: Meaghan Lewis

src/GitHub.VisualStudio.UI/Views/ViewLocator.cs

@@ -32,10 +32,16 @@ public class ViewLocator : IValueConverter
         /// <param name="culture">Unused.</param>
         /// <returns>
         /// A new instance of a view for the specified view model, or an error string if a view
-        /// could not be located.
+        /// could not be located. A null view model will return null.
         /// </returns>
         public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
         {
+            if (value == null)
+            {
+                // Return null for a null view model
+                return null;
+            }
+
             var exportViewModelAttribute = value.GetType().GetCustomAttributes(typeof(ExportAttribute), false)
                 .OfType<ExportAttribute>()
                 .Where(x => typeof(IViewModel).IsAssignableFrom(x.ContractType))