Apply suggestions from code review

Emby.Server.Implementations/HttpServer/WebSocketConnection.cs

@@ -209,7 +209,7 @@ namespace Emby.Server.Implementations.HttpServer
                 return;
             }
 
-            if (stub is null)
+            if (stub == null)
             {
                 _logger.LogError("Error processing web socket message");
                 return;

Jellyfin.Server/Migrations/Routines/MigrateUserDb.cs

@@ -75,7 +75,7 @@ namespace Jellyfin.Server.Migrations.Routines
                 foreach (var entry in queryResult)
                 {
                     UserMockup? mockup = JsonSerializer.Deserialize<UserMockup>(entry[2].ToBlob(), JsonDefaults.GetOptions());
-                    if (mockup is null)
+                    if (mockup == null)
                     {
                         continue;
                     }