U4-9201 - troubleshoot

src/Umbraco.Core/Persistence/UmbracoDatabase.cs

@@ -247,6 +247,7 @@ namespace Umbraco.Core.Persistence
 
         protected override void Dispose(bool disposing)
         {
+            base.Dispose(disposing);
             LogHelper.Debug<UmbracoDatabase>("Dispose (" + InstanceSid + ").");
             if (DatabaseFactory != null) DatabaseFactory.OnDispose(this);
         }

src/Umbraco.Core/UmbracoApplicationBase.cs

@@ -63,7 +63,9 @@ namespace Umbraco.Core
             // after Umbraco has started there is a database in "context" and that context is
             // going to stay there and never get destroyed nor reused, so we have to ensure that
             // the database is disposed (which will auto-remove it from context).
-            ApplicationContext.Current.DatabaseContext.Database.Dispose();
+            var database = ApplicationContext.Current.DatabaseContext.Database;
+            if (database != null) // never to happen... unless in weird tests
+                ApplicationContext.Current.DatabaseContext.Database.Dispose();
         }
 
         /// <summary>