Singer in the Singer avatar should be nullable.

osu.Game.Rulesets.Karaoke/Graphics/Sprites/DrawableCircleSingerAvatar.cs

@@ -4,7 +4,7 @@
 using System;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
-using osu.Framework.Graphics.Textures;
+using osu.Game.Graphics;
 using osu.Game.Rulesets.Karaoke.Beatmaps.Metadatas;
 using osu.Game.Rulesets.Karaoke.Beatmaps.Metadatas.Types;
 using osu.Game.Rulesets.Karaoke.Beatmaps.Utils;
@@ -16,19 +16,19 @@ public partial class DrawableCircleSingerAvatar : DrawableSingerAvatar
     private readonly IBindable<float> bindableHue = new Bindable<float>();
 
     [BackgroundDependencyLoader]
-    private void load(LargeTextureStore textures)
+    private void load(OsuColour colour)
     {
         Masking = true;
         CornerRadius = Math.Min(DrawSize.X, DrawSize.Y) / 2f;
         BorderThickness = 5;
 
         bindableHue.BindValueChanged(_ =>
         {
-            BorderColour = SingerUtils.GetContentColour(Singer);
+            BorderColour = Singer != null ? SingerUtils.GetContentColour(Singer) : colour.Gray0;
         }, true);
     }
 
-    public override ISinger Singer
+    public override ISinger? Singer
     {
         get => base.Singer;
         set

osu.Game.Rulesets.Karaoke/Graphics/UserInterface/SingerDisplay.cs

@@ -133,7 +133,7 @@ private partial class DrawableSinger : DrawableCircleSingerAvatar, IHasCustomToo
     {
         public ITooltip<ISinger> GetCustomTooltip() => new SingerToolTip();
 
-        public ISinger TooltipContent => Singer;
+        public ISinger? TooltipContent => Singer;
     }
 }