diff --git a/osu.Game.Rulesets.Karaoke/Beatmaps/Stages/Preview/PreviewLyricLayoutCategory.cs b/osu.Game.Rulesets.Karaoke/Beatmaps/Stages/Preview/PreviewLyricLayoutCategory.cs
index 88644cd9c..61caa772d 100644
--- a/osu.Game.Rulesets.Karaoke/Beatmaps/Stages/Preview/PreviewLyricLayoutCategory.cs
+++ b/osu.Game.Rulesets.Karaoke/Beatmaps/Stages/Preview/PreviewLyricLayoutCategory.cs
@@ -8,9 +8,4 @@ namespace osu.Game.Rulesets.Karaoke.Beatmaps.Stages.Preview;
 public class PreviewLyricLayoutCategory : StageElementCategory<PreviewLyricLayout, Lyric>
 {
     protected override PreviewLyricLayout CreateElement(int id) => new(id);
-
-    public void ReCalculate()
-    {
-        // todo: do something.
-    }
 }
diff --git a/osu.Game.Rulesets.Karaoke/Configuration/KaraokeRulesetConfigManager.cs b/osu.Game.Rulesets.Karaoke/Configuration/KaraokeRulesetConfigManager.cs
index 0c458aee9..a0a10de65 100644
--- a/osu.Game.Rulesets.Karaoke/Configuration/KaraokeRulesetConfigManager.cs
+++ b/osu.Game.Rulesets.Karaoke/Configuration/KaraokeRulesetConfigManager.cs
@@ -16,7 +16,7 @@ namespace osu.Game.Rulesets.Karaoke.Configuration
 {
     public class KaraokeRulesetConfigManager : RulesetConfigManager<KaraokeRulesetSetting>
     {
-        public KaraokeRulesetConfigManager(SettingsStore settings, RulesetInfo ruleset, int? variant = null)
+        public KaraokeRulesetConfigManager(SettingsStore? settings, RulesetInfo ruleset, int? variant = null)
             : base(settings, ruleset, variant)
         {
         }
diff --git a/osu.Game.Rulesets.Karaoke/KaraokeRuleset.cs b/osu.Game.Rulesets.Karaoke/KaraokeRuleset.cs
index 42a7d1c52..bb5e0d0aa 100644
--- a/osu.Game.Rulesets.Karaoke/KaraokeRuleset.cs
+++ b/osu.Game.Rulesets.Karaoke/KaraokeRuleset.cs
@@ -1,8 +1,6 @@
 // Copyright (c) andy840119 <andy840119@gmail.com>. Licensed under the GPL Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 using osu.Framework.Allocation;
@@ -51,7 +49,7 @@ namespace osu.Game.Rulesets.Karaoke
     [ExcludeFromDynamicCompile]
     public partial class KaraokeRuleset : Ruleset
     {
-        public override DrawableRuleset CreateDrawableRulesetWith(IBeatmap beatmap, IReadOnlyList<Mod> mods = null) => new DrawableKaraokeRuleset(this, beatmap, mods);
+        public override DrawableRuleset CreateDrawableRulesetWith(IBeatmap beatmap, IReadOnlyList<Mod>? mods = null) => new DrawableKaraokeRuleset(this, beatmap, mods);
         public override ScoreProcessor CreateScoreProcessor() => new KaraokeScoreProcessor();
         public override IBeatmapConverter CreateBeatmapConverter(IBeatmap beatmap) => new KaraokeBeatmapConverter(beatmap, this);
         public override IBeatmapProcessor CreateBeatmapProcessor(IBeatmap beatmap) => new KaraokeBeatmapProcessor(beatmap);
@@ -208,13 +206,13 @@ public override ISkin CreateSkinTransformer(ISkin skin, IBeatmap beatmap)
                 ArgonSkin => new KaraokeArgonSkinTransformer(skin, beatmap),
                 DefaultLegacySkin => new KaraokeClassicSkinTransformer(skin, beatmap),
                 LegacySkin => new KaraokeLegacySkinTransformer(skin, beatmap),
-                _ => null
+                _ => throw new InvalidOperationException(),
             };
         }
 
         public override IConvertibleReplayFrame CreateConvertibleReplayFrame() => new KaraokeReplayFrame();
 
-        public override IRulesetConfigManager CreateConfig(SettingsStore settings) => new KaraokeRulesetConfigManager(settings, RulesetInfo);
+        public override IRulesetConfigManager CreateConfig(SettingsStore? settings) => new KaraokeRulesetConfigManager(settings, RulesetInfo);
 
         public override RulesetSettingsSubsection CreateSettings() => new KaraokeSettingsSubsection(this);