diff --git a/osu.Game.Rulesets.Karaoke.Tests/Resources/TestResources.cs b/osu.Game.Rulesets.Karaoke.Tests/Resources/TestResources.cs
index 3c99baf34..fa77e3166 100644
--- a/osu.Game.Rulesets.Karaoke.Tests/Resources/TestResources.cs
+++ b/osu.Game.Rulesets.Karaoke.Tests/Resources/TestResources.cs
@@ -44,8 +44,6 @@ public static string GetTestLrcForImport(string name)
 
     public static IStorageResourceProvider CreateSkinStorageResourceProvider(string skinName = "special-skin") => new TestStorageResourceProvider(skinName);
 
-#nullable disable
-
     private class TestStorageResourceProvider : IStorageResourceProvider
     {
         public TestStorageResourceProvider(string skinName)
@@ -55,13 +53,11 @@ public TestStorageResourceProvider(string skinName)
 
         public IRenderer Renderer => new DummyRenderer();
 
-        public AudioManager AudioManager => null;
+        public AudioManager AudioManager => null!;
         public IResourceStore<byte[]> Files { get; }
         public IResourceStore<byte[]> Resources { get; }
-        public RealmAccess RealmAccess => null;
+        public RealmAccess RealmAccess => null!;
 
-        public IResourceStore<TextureUpload> CreateTextureLoaderStore(IResourceStore<byte[]> underlyingStore) => null;
+        public IResourceStore<TextureUpload> CreateTextureLoaderStore(IResourceStore<byte[]> underlyingStore) => null!;
     }
-
-#nullable enable
 }
diff --git a/osu.Game.Rulesets.Karaoke.Tests/Skinning/Fonts/BitmapFontCompressorTest.cs b/osu.Game.Rulesets.Karaoke.Tests/Skinning/Fonts/BitmapFontCompressorTest.cs
index bb4bf9224..82bdabfc1 100644
--- a/osu.Game.Rulesets.Karaoke.Tests/Skinning/Fonts/BitmapFontCompressorTest.cs
+++ b/osu.Game.Rulesets.Karaoke.Tests/Skinning/Fonts/BitmapFontCompressorTest.cs
@@ -31,7 +31,7 @@ public void OneTimeSetUp()
         if (normalGlyph == null)
             throw new ArgumentNullException(nameof(normalGlyph));
 
-        font = glyphStore.BitmapFont;
+        font = glyphStore.BitmapFont ?? throw new InvalidOperationException("Font should not be null in the test case.");
     }
 
     [TestCase("A", 1)]
diff --git a/osu.Game.Rulesets.Karaoke.Tests/Skinning/Fonts/BitmapFontImageGeneratorTest.cs b/osu.Game.Rulesets.Karaoke.Tests/Skinning/Fonts/BitmapFontImageGeneratorTest.cs
index 0262c9565..54370f112 100644
--- a/osu.Game.Rulesets.Karaoke.Tests/Skinning/Fonts/BitmapFontImageGeneratorTest.cs
+++ b/osu.Game.Rulesets.Karaoke.Tests/Skinning/Fonts/BitmapFontImageGeneratorTest.cs
@@ -18,7 +18,7 @@ public class BitmapFontImageGeneratorTest
 {
     private TestFntGlyphStore glyphStore = null!;
 
-    private BitmapFont font => glyphStore.BitmapFont;
+    private BitmapFont font = null!;
 
     [OneTimeSetUp]
     public void OneTimeSetUp()
@@ -31,6 +31,8 @@ public void OneTimeSetUp()
         var normalGlyph = glyphStore.Get('a');
         if (normalGlyph == null)
             throw new ArgumentNullException(nameof(normalGlyph));
+
+        font = glyphStore.BitmapFont ?? throw new InvalidOperationException("Font should not be null in the test case.");
     }
 
     [Test]
diff --git a/osu.Game.Rulesets.Karaoke/IO/Archives/CachedFontArchiveReader.cs b/osu.Game.Rulesets.Karaoke/IO/Archives/CachedFontArchiveReader.cs
index 9b157aff4..e67dd7b4e 100644
--- a/osu.Game.Rulesets.Karaoke/IO/Archives/CachedFontArchiveReader.cs
+++ b/osu.Game.Rulesets.Karaoke/IO/Archives/CachedFontArchiveReader.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.Collections.Generic;
 using System.IO;
 using System.Linq;
@@ -22,7 +20,7 @@ public class CachedFontArchiveReader : ArchiveReader
     private readonly Stream archiveStream;
     private readonly ZipArchive archive;
 
-    public CachedFontArchiveReader(Stream archiveStream, string name = null)
+    public CachedFontArchiveReader(Stream archiveStream, string name)
         : base(name)
     {
         this.archiveStream = archiveStream;
diff --git a/osu.Game.Rulesets.Karaoke/IO/Stores/FntGlyphStore.cs b/osu.Game.Rulesets.Karaoke/IO/Stores/FntGlyphStore.cs
index 5b231434a..1eecb2422 100644
--- a/osu.Game.Rulesets.Karaoke/IO/Stores/FntGlyphStore.cs
+++ b/osu.Game.Rulesets.Karaoke/IO/Stores/FntGlyphStore.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 osu.Framework.Graphics.Textures;
 using osu.Framework.IO.Stores;
 using SharpFNT;
@@ -11,9 +9,9 @@ namespace osu.Game.Rulesets.Karaoke.IO.Stores;
 
 public class FntGlyphStore : GlyphStore
 {
-    public BitmapFont BitmapFont => Font;
+    public BitmapFont? BitmapFont => Font;
 
-    public FntGlyphStore(ResourceStore<byte[]> store, string assetName = null, IResourceStore<TextureUpload> textureLoader = null)
+    public FntGlyphStore(ResourceStore<byte[]> store, string? assetName = null, IResourceStore<TextureUpload>? textureLoader = null)
         : base(store, assetName, textureLoader)
     {
     }
diff --git a/osu.Game.Rulesets.Karaoke/IO/Stores/KaraokeLocalFontStore.cs b/osu.Game.Rulesets.Karaoke/IO/Stores/KaraokeLocalFontStore.cs
index 73c681d22..9ece0a89e 100644
--- a/osu.Game.Rulesets.Karaoke/IO/Stores/KaraokeLocalFontStore.cs
+++ b/osu.Game.Rulesets.Karaoke/IO/Stores/KaraokeLocalFontStore.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.Collections.Generic;
 using osu.Framework.Graphics.Rendering;
 using osu.Framework.Graphics.Sprites;
@@ -25,7 +23,7 @@ public class KaraokeLocalFontStore : FontStore
     /// <param name="renderer">The renderer to create textures with.</param>
     /// <param name="store">The texture source.</param>
     /// <param name="scaleAdjust">The raw pixel height of the font. Can be used to apply a global scale or metric to font usages.</param>
-    public KaraokeLocalFontStore(FontManager fontManager, IRenderer renderer, IResourceStore<TextureUpload> store = null, float scaleAdjust = 100)
+    public KaraokeLocalFontStore(FontManager fontManager, IRenderer renderer, IResourceStore<TextureUpload>? store = null, float scaleAdjust = 100)
         : base(renderer, store, scaleAdjust)
     {
         this.fontManager = fontManager;
diff --git a/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableBarLine.cs b/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableBarLine.cs
index f0981d087..0145a3128 100644
--- a/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableBarLine.cs
+++ b/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableBarLine.cs
@@ -1,9 +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 JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
@@ -33,12 +30,12 @@ public partial class DrawableBarLine : DrawableKaraokeScrollingHitObject<BarLine
     /// <summary>
     /// The visual line tracker.
     /// </summary>
-    private Box line;
+    private Box line = null!;
 
     /// <summary>
     /// Container with triangles. Only visible for major lines.
     /// </summary>
-    private Container triangleContainer;
+    private Container triangleContainer = null!;
 
     private readonly Bindable<bool> major = new();
 
@@ -47,7 +44,7 @@ public DrawableBarLine()
     {
     }
 
-    public DrawableBarLine([CanBeNull] BarLine barLine)
+    public DrawableBarLine(BarLine? barLine)
         : base(barLine)
     {
     }
diff --git a/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableKaraokeHitObject.cs b/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableKaraokeHitObject.cs
index b2c5c54fa..569719f25 100644
--- a/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableKaraokeHitObject.cs
+++ b/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableKaraokeHitObject.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 osu.Game.Rulesets.Judgements;
 using osu.Game.Rulesets.Karaoke.Judgements;
 using osu.Game.Rulesets.Karaoke.Objects.Types;
@@ -12,8 +10,8 @@ namespace osu.Game.Rulesets.Karaoke.Objects.Drawables;
 
 public partial class DrawableKaraokeHitObject : DrawableHitObject<KaraokeHitObject>
 {
-    protected DrawableKaraokeHitObject(KaraokeHitObject hitObject)
-        : base(hitObject)
+    protected DrawableKaraokeHitObject(KaraokeHitObject? hitObject)
+        : base(hitObject!)
     {
     }
 
diff --git a/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableKaraokeScrollingHitObject.cs b/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableKaraokeScrollingHitObject.cs
index 14654ebe0..415e3af86 100644
--- a/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableKaraokeScrollingHitObject.cs
+++ b/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableKaraokeScrollingHitObject.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 osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
@@ -17,8 +15,8 @@ public abstract partial class DrawableKaraokeScrollingHitObject : DrawableHitObj
 
     protected readonly IBindable<double> TimeRange = new Bindable<double>();
 
-    protected DrawableKaraokeScrollingHitObject(KaraokeHitObject hitObject)
-        : base(hitObject)
+    protected DrawableKaraokeScrollingHitObject(KaraokeHitObject? hitObject)
+        : base(hitObject!)
     {
     }
 
@@ -102,9 +100,9 @@ protected virtual void OnTimeRangeChanged(ValueChangedEvent<double> e)
 public abstract partial class DrawableKaraokeScrollingHitObject<TObject> : DrawableKaraokeScrollingHitObject
     where TObject : KaraokeHitObject
 {
-    public new TObject HitObject => base.HitObject as TObject;
+    public new TObject HitObject => (TObject)base.HitObject;
 
-    protected DrawableKaraokeScrollingHitObject(TObject hitObject)
+    protected DrawableKaraokeScrollingHitObject(TObject? hitObject)
         : base(hitObject)
     {
     }
diff --git a/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableLyric.cs b/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableLyric.cs
index c6333235c..0405e1837 100644
--- a/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableLyric.cs
+++ b/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableLyric.cs
@@ -1,11 +1,8 @@
 // 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.Globalization;
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Extensions.IEnumerableExtensions;
@@ -24,11 +21,10 @@ namespace osu.Game.Rulesets.Karaoke.Objects.Drawables;
 
 public partial class DrawableLyric : DrawableKaraokeHitObject
 {
-    private Container<DrawableKaraokeSpriteText> lyricPieces;
-    private OsuSpriteText translateText;
+    private Container<DrawableKaraokeSpriteText> lyricPieces = null!;
+    private OsuSpriteText translateText = null!;
 
-    [Resolved(canBeNull: true)]
-    private KaraokeRulesetConfigManager config { get; set; }
+    private KaraokeRulesetConfigManager? config { get; set; }
 
     private readonly BindableBool useTranslateBindable = new();
     private readonly Bindable<CultureInfo> preferLanguageBindable = new();
@@ -43,8 +39,8 @@ public partial class DrawableLyric : DrawableKaraokeHitObject
     private readonly IBindableDictionary<Singer, SingerState[]> singersBindable = new BindableDictionary<Singer, SingerState[]>();
     private readonly BindableDictionary<CultureInfo, string> translateTextBindable = new();
 
-    public event Action<DrawableLyric> OnLyricStart;
-    public event Action<DrawableLyric> OnLyricEnd;
+    public event Action<DrawableLyric>? OnLyricStart;
+    public event Action<DrawableLyric>? OnLyricEnd;
 
     public new Lyric HitObject => (Lyric)base.HitObject;
 
@@ -53,13 +49,13 @@ public DrawableLyric()
     {
     }
 
-    public DrawableLyric([CanBeNull] Lyric hitObject)
+    public DrawableLyric(Lyric? hitObject)
         : base(hitObject)
     {
     }
 
     [BackgroundDependencyLoader(true)]
-    private void load([CanBeNull] KaraokeSessionStatics session)
+    private void load(KaraokeSessionStatics? session)
     {
         AutoSizeAxes = Axes.Both;
 
@@ -180,11 +176,11 @@ private void applyTranslate()
 
         if (!needTranslate || language == null)
         {
-            translateText.Text = (string)null;
+            translateText.Text = string.Empty;
         }
         else
         {
-            if (translateTextBindable.TryGetValue(language, out string translate))
+            if (translateTextBindable.TryGetValue(language, out string? translate))
                 translateText.Text = translate;
         }
     }
diff --git a/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableNote.cs b/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableNote.cs
index 0fd587855..4b3293827 100644
--- a/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableNote.cs
+++ b/osu.Game.Rulesets.Karaoke/Objects/Drawables/DrawableNote.cs
@@ -1,11 +1,8 @@
 // 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.Diagnostics;
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
@@ -44,7 +41,7 @@ public partial class DrawableNote : DrawableKaraokeScrollingHitObject<Note>, IKe
     private readonly IBindable<NotePositionCalculator> positionBindable = new Bindable<NotePositionCalculator>();
 
     public readonly IBindable<string> TextBindable = new Bindable<string>();
-    public readonly IBindable<string> RubyTextBindable = new Bindable<string>();
+    public readonly IBindable<string?> RubyTextBindable = new Bindable<string?>();
     public readonly IBindableDictionary<Singer, SingerState[]> SingersBindable = new BindableDictionary<Singer, SingerState[]>();
     public readonly IBindable<bool> DisplayBindable = new Bindable<bool>();
     public readonly IBindable<Tone> ToneBindable = new Bindable<Tone>();
@@ -54,7 +51,7 @@ public DrawableNote()
     {
     }
 
-    public DrawableNote([CanBeNull] Note hitObject)
+    public DrawableNote(Note? hitObject)
         : base(hitObject)
     {
         AddRangeInternal(new Drawable[]
@@ -81,7 +78,7 @@ private void load(INotePositionInfo notePositionInfo)
         TextBindable.BindValueChanged(_ => { changeText(HitObject); });
         RubyTextBindable.BindValueChanged(_ => { changeText(HitObject); });
         SingersBindable.BindCollectionChanged((_, _) => { ApplySkin(CurrentSkin, false); });
-        DisplayBindable.BindValueChanged(e => { (Result.Judgement as KaraokeNoteJudgement).Scorable = e.NewValue; });
+        DisplayBindable.BindValueChanged(e => { (Result.Judgement as KaraokeNoteJudgement)!.Scorable = e.NewValue; });
         ToneBindable.BindValueChanged(_ => updateNotePositionAndHeight());
 
         void updateNotePositionAndHeight()
diff --git a/osu.Game.Rulesets.Karaoke/Skinning/InternalSkinStorageResourceProvider.cs b/osu.Game.Rulesets.Karaoke/Skinning/InternalSkinStorageResourceProvider.cs
index ae58248ff..002fb2d54 100644
--- a/osu.Game.Rulesets.Karaoke/Skinning/InternalSkinStorageResourceProvider.cs
+++ b/osu.Game.Rulesets.Karaoke/Skinning/InternalSkinStorageResourceProvider.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 osu.Framework.Audio;
 using osu.Framework.Graphics.Rendering;
 using osu.Framework.Graphics.Rendering.Dummy;
@@ -23,9 +21,9 @@ public InternalSkinStorageResourceProvider(string skinName)
 
     public IRenderer Renderer => new DummyRenderer();
 
-    public AudioManager AudioManager => null;
+    public AudioManager AudioManager => null!;
     public IResourceStore<byte[]> Files { get; }
     public IResourceStore<byte[]> Resources { get; }
-    public RealmAccess RealmAccess => null;
-    public IResourceStore<TextureUpload> CreateTextureLoaderStore(IResourceStore<byte[]> underlyingStore) => null;
+    public RealmAccess RealmAccess => null!;
+    public IResourceStore<TextureUpload> CreateTextureLoaderStore(IResourceStore<byte[]> underlyingStore) => null!;
 }