Resolve new nullability warnings

Author: huoyaoyuan

osu.Game/Graphics/UserInterface/DrawableStatefulMenuItem.cs

@@ -37,7 +37,7 @@ protected override bool OnMouseDown(MouseDownEvent e)
         private partial class ToggleTextContainer : TextContainer
         {
             private readonly StatefulMenuItem menuItem;
-            private readonly Bindable<object> state;
+            private readonly Bindable<object?> state;
             private readonly SpriteIcon stateIcon;
 
             public ToggleTextContainer(StatefulMenuItem menuItem)
@@ -61,7 +61,7 @@ protected override void LoadComplete()
                 state.BindValueChanged(updateState, true);
             }
 
-            private void updateState(ValueChangedEvent<object> state)
+            private void updateState(ValueChangedEvent<object?> state)
             {
                 var icon = menuItem.GetIconForState(state.NewValue);
 

osu.Game/Graphics/UserInterface/StatefulMenuItem.cs

@@ -53,7 +53,7 @@ protected StatefulMenuItem(LocalisableString text, Func<object?, object?>? chang
         /// </summary>
         /// <param name="state">The state to retrieve the relevant icon for.</param>
         /// <returns>The icon to be displayed for <paramref name="state"/>.</returns>
-        public abstract IconUsage? GetIconForState(object state);
+        public abstract IconUsage? GetIconForState(object? state);
     }
 
     public abstract class StatefulMenuItem<T> : StatefulMenuItem
@@ -97,7 +97,7 @@ protected StatefulMenuItem(LocalisableString text, Func<T, T>? changeStateFunc,
             State.BindValueChanged(state => base.State.Value = state.NewValue);
         }
 
-        public sealed override IconUsage? GetIconForState(object state) => GetIconForState((T)state);
+        public sealed override IconUsage? GetIconForState(object? state) => GetIconForState((T)state!);
 
         /// <summary>
         /// Retrieves the icon to be displayed for a state.

osu.Game/Screens/Edit/Setup/ColoursSection.cs

@@ -66,7 +66,7 @@ protected override void LoadComplete()
                 syncingColours = true;
 
                 comboColours.Colours.Clear();
-                comboColours.Colours.AddRange(Beatmap.BeatmapSkin?.ComboColours);
+                comboColours.Colours.AddRange(Beatmap.BeatmapSkin?.ComboColours ?? []);
 
                 syncingColours = false;
             });

osu.Game/Screens/OnlinePlay/Match/DrawableMatchRoom.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.ComponentModel;
+using System.Diagnostics;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
@@ -38,6 +39,10 @@ public DrawableMatchRoom(Room room, bool allowEdit = true)
         {
             this.allowEdit = allowEdit;
 
+            // Roslyn sees required non-nullable property as nullable in constructor,
+            // as it can't see the implementation provides a fallback.
+            Debug.Assert(SelectedItem != null);
+
             base.SelectedItem.BindTo(SelectedItem);
         }
 

osu.Game/Screens/Select/SongSelect.cs

@@ -994,7 +994,7 @@ private void bindBindables()
 
             selectedMods.BindValueChanged(_ =>
             {
-                if (decoupledRuleset.Value.Equals(rulesetNoDebounce))
+                if (decoupledRuleset.Value?.Equals(rulesetNoDebounce) ?? false)
                     advancedStats.Mods.Value = selectedMods.Value;
             }, true);