Use quick way to fix this issue.

DI object might be null in the dispose method.

see:
- ppy/osu@b11ae1c

osu.Game.Rulesets.Karaoke/Screens/Edit/Beatmaps/Lyrics/LyricEditorVerifier.cs

@@ -7,6 +7,7 @@
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Caching;
+using osu.Framework.Extensions.ObjectExtensions;
 using osu.Game.Beatmaps;
 using osu.Game.Rulesets.Edit;
 using osu.Game.Rulesets.Edit.Checks.Components;
@@ -182,6 +183,10 @@ protected override void Dispose(bool isDisposing)
     {
         base.Dispose(isDisposing);
 
+        // todo: not very sure
+        if (!editorBeatmap.IsNull())
+            return;
+
         editorBeatmap.HitObjectAdded -= hitObjectAdded;
         editorBeatmap.HitObjectRemoved -= hitObjectRemoved;
         editorBeatmap.HitObjectUpdated -= hitObjectUpdated;