Manual fixes to reduce warnings to zero

osu.Game.Rulesets.Mania.Tests/Editor/ManiaSelectionBlueprintTestScene.cs

@@ -17,7 +17,7 @@ namespace osu.Game.Rulesets.Mania.Tests.Editor
     {
         protected override Container<Drawable> Content => blueprints ?? base.Content;
 
-        private readonly Container blueprints;
+        private readonly Container? blueprints;
 
         [Cached(typeof(Playfield))]
         public Playfield Playfield { get; }

osu.Game.Rulesets.Mania.Tests/ManiaInputTestScene.cs

@@ -12,7 +12,8 @@ namespace osu.Game.Rulesets.Mania.Tests
 {
     public abstract partial class ManiaInputTestScene : OsuTestScene
     {
-        private readonly Container<Drawable> content;
+        private readonly Container<Drawable>? content;
+
         protected override Container<Drawable> Content => content ?? base.Content;
 
         protected ManiaInputTestScene(int keys)

osu.Game.Rulesets.Mania/Edit/ManiaBlueprintContainer.cs

@@ -16,7 +16,7 @@ namespace osu.Game.Rulesets.Mania.Edit
         {
         }
 
-        public override HitObjectSelectionBlueprint CreateHitObjectBlueprintFor(HitObject hitObject)
+        public override HitObjectSelectionBlueprint? CreateHitObjectBlueprintFor(HitObject hitObject)
         {
             switch (hitObject)
             {

osu.Game.Rulesets.Osu/Difficulty/Preprocessing/OsuDifficultyHitObject.cs

@@ -82,13 +82,13 @@ namespace osu.Game.Rulesets.Osu.Difficulty.Preprocessing
         /// </summary>
         public double HitWindowGreat { get; private set; }
 
-        private readonly OsuHitObject lastLastObject;
+        private readonly OsuHitObject? lastLastObject;
         private readonly OsuHitObject lastObject;
 
-        public OsuDifficultyHitObject(HitObject hitObject, HitObject lastObject, HitObject lastLastObject, double clockRate, List<DifficultyHitObject> objects, int index)
+        public OsuDifficultyHitObject(HitObject hitObject, HitObject lastObject, HitObject? lastLastObject, double clockRate, List<DifficultyHitObject> objects, int index)
             : base(hitObject, lastObject, clockRate, objects, index)
         {
-            this.lastLastObject = (OsuHitObject)lastLastObject;
+            this.lastLastObject = lastLastObject as OsuHitObject;
             this.lastObject = (OsuHitObject)lastObject;
 
             // Capped to 25ms to prevent difficulty calculation breaking from simultaneous objects.

osu.Game.Rulesets.Osu/Edit/OsuBlueprintContainer.cs

@@ -20,7 +20,7 @@ namespace osu.Game.Rulesets.Osu.Edit
 
         protected override SelectionHandler<HitObject> CreateSelectionHandler() => new OsuSelectionHandler();
 
-        public override HitObjectSelectionBlueprint CreateHitObjectBlueprintFor(HitObject hitObject)
+        public override HitObjectSelectionBlueprint? CreateHitObjectBlueprintFor(HitObject hitObject)
         {
             switch (hitObject)
             {

osu.Game.Rulesets.Taiko/Objects/Drawables/DrawableStrongNestedHit.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using JetBrains.Annotations;
 using osu.Game.Rulesets.Taiko.Judgements;
 
 namespace osu.Game.Rulesets.Taiko.Objects.Drawables
@@ -11,9 +10,9 @@ namespace osu.Game.Rulesets.Taiko.Objects.Drawables
     /// </summary>
     public abstract partial class DrawableStrongNestedHit : DrawableTaikoHitObject
     {
-        public new DrawableTaikoHitObject ParentHitObject => (DrawableTaikoHitObject)base.ParentHitObject;
+        public new DrawableTaikoHitObject? ParentHitObject => base.ParentHitObject as DrawableTaikoHitObject;
 
-        protected DrawableStrongNestedHit([CanBeNull] StrongNestedHitObject nestedHit)
+        protected DrawableStrongNestedHit(StrongNestedHitObject? nestedHit)
             : base(nestedHit)
         {
         }

osu.Game.Tests/Visual/Editing/TestSceneHitObjectSampleAdjustments.cs

@@ -358,7 +358,7 @@ namespace osu.Game.Tests.Visual.Editing
             var popover = this.ChildrenOfType<SamplePointPiece.SampleEditPopover>().SingleOrDefault();
             var textBox = popover?.ChildrenOfType<OsuTextBox>().First();
 
-            return textBox?.Current.Value == bank && string.IsNullOrEmpty(textBox?.PlaceholderText.ToString());
+            return textBox?.Current.Value == bank && string.IsNullOrEmpty(textBox.PlaceholderText.ToString());
         });
 
         private void samplePopoverHasIndeterminateBank() => AddUntilStep("sample popover has indeterminate bank", () =>

osu.Game.Tournament.Tests/Screens/TestSceneTeamWinScreen.cs

@@ -15,7 +15,7 @@ namespace osu.Game.Tournament.Tests.Screens
         {
             AddStep("set up match", () =>
             {
-                var match = Ladder.CurrentMatch.Value;
+                var match = Ladder.CurrentMatch.Value!;
 
                 match.Round.Value = Ladder.Rounds.FirstOrDefault(g => g.Name.Value == "Finals");
                 match.Completed.Value = true;

osu.Game.Tournament/Components/DrawableTeamTitleWithHeader.cs

@@ -10,7 +10,7 @@ namespace osu.Game.Tournament.Components
 {
     public partial class DrawableTeamTitleWithHeader : CompositeDrawable
     {
-        public DrawableTeamTitleWithHeader(TournamentTeam team, TeamColour colour)
+        public DrawableTeamTitleWithHeader(TournamentTeam? team, TeamColour colour)
         {
             AutoSizeAxes = Axes.Both;
 

osu.Game.Tournament/Components/DrawableTeamWithPlayers.cs

@@ -13,7 +13,7 @@ namespace osu.Game.Tournament.Components
 {
     public partial class DrawableTeamWithPlayers : CompositeDrawable
     {
-        public DrawableTeamWithPlayers(TournamentTeam team, TeamColour colour)
+        public DrawableTeamWithPlayers(TournamentTeam? team, TeamColour colour)
         {
             AutoSizeAxes = Axes.Both;
 

osu.Game.Tournament/Models/LadderInfo.cs

@@ -25,7 +25,7 @@ namespace osu.Game.Tournament.Models
         public List<TournamentProgression> Progressions = new List<TournamentProgression>();
 
         [JsonIgnore] // updated manually in TournamentGameBase
-        public Bindable<TournamentMatch> CurrentMatch = new Bindable<TournamentMatch>();
+        public Bindable<TournamentMatch?> CurrentMatch = new Bindable<TournamentMatch?>();
 
         public Bindable<int> ChromaKeyWidth = new BindableInt(1024)
         {

osu.Game.Tournament/Screens/Gameplay/Components/MatchRoundDisplay.cs

@@ -10,7 +10,7 @@ namespace osu.Game.Tournament.Screens.Gameplay.Components
 {
     public partial class MatchRoundDisplay : TournamentSpriteTextWithBackground
     {
-        private readonly Bindable<TournamentMatch> currentMatch = new Bindable<TournamentMatch>();
+        private readonly Bindable<TournamentMatch?> currentMatch = new Bindable<TournamentMatch?>();
 
         [BackgroundDependencyLoader]
         private void load(LadderInfo ladder)
@@ -19,7 +19,7 @@ namespace osu.Game.Tournament.Screens.Gameplay.Components
             currentMatch.BindTo(ladder.CurrentMatch);
         }
 
-        private void matchChanged(ValueChangedEvent<TournamentMatch> match) =>
+        private void matchChanged(ValueChangedEvent<TournamentMatch?> match) =>
             Text.Text = match.NewValue?.Round.Value?.Name.Value ?? "Unknown Round";
     }
 }

osu.Game/Beatmaps/APIFailTimes.cs

@@ -15,12 +15,12 @@ namespace osu.Game.Beatmaps
         /// Points of failure on a relative time scale (usually 0..100).
         /// </summary>
         [JsonProperty(@"fail")]
-        public int[] Fails { get; set; } = Array.Empty<int>();
+        public int[]? Fails { get; set; } = Array.Empty<int>();
 
         /// <summary>
         /// Points of retry on a relative time scale (usually 0..100).
         /// </summary>
         [JsonProperty(@"exit")]
-        public int[] Retries { get; set; } = Array.Empty<int>();
+        public int[]? Retries { get; set; } = Array.Empty<int>();
     }
 }

osu.Game/Beatmaps/Drawables/UpdateableBeatmapBackgroundSprite.cs

@@ -50,7 +50,7 @@ namespace osu.Game.Beatmaps.Drawables
             return drawable;
         }
 
-        private Drawable getDrawableForModel(IBeatmapInfo model)
+        private Drawable getDrawableForModel(IBeatmapInfo? model)
         {
             // prefer online cover where available.
             if (model?.BeatmapSet is IBeatmapSetOnlineInfo online)

osu.Game/Beatmaps/Legacy/LegacyControlPointInfo.cs

@@ -2,7 +2,6 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System.Collections.Generic;
-using JetBrains.Annotations;
 using Newtonsoft.Json;
 using osu.Framework.Lists;
 using osu.Game.Beatmaps.ControlPoints;
@@ -24,7 +23,6 @@ namespace osu.Game.Beatmaps.Legacy
         /// </summary>
         /// <param name="time">The time to find the sound control point at.</param>
         /// <returns>The sound control point.</returns>
-        [NotNull]
         public SampleControlPoint SamplePointAt(double time) => BinarySearchWithFallback(SamplePoints, time, SamplePoints.Count > 0 ? SamplePoints[0] : SampleControlPoint.DEFAULT);
 
         /// <summary>
@@ -40,7 +38,6 @@ namespace osu.Game.Beatmaps.Legacy
         /// </summary>
         /// <param name="time">The time to find the difficulty control point at.</param>
         /// <returns>The difficulty control point.</returns>
-        [NotNull]
         public DifficultyControlPoint DifficultyPointAt(double time) => BinarySearchWithFallback(DifficultyPoints, time, DifficultyControlPoint.DEFAULT);
 
         public override void Clear()

osu.Game/Configuration/OsuConfigManager.cs

@@ -257,7 +257,7 @@ namespace osu.Game.Configuration
                     string skinName = string.Empty;
 
                     if (Guid.TryParse(skin, out var id))
-                        skinName = LookupSkinName(id) ?? string.Empty;
+                        skinName = LookupSkinName(id);
 
                     return new SettingDescription(
                         rawValue: skinName,

osu.Game/Database/IHasFiles.cs

@@ -2,7 +2,6 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System.Collections.Generic;
-using JetBrains.Annotations;
 
 namespace osu.Game.Database
 {
@@ -13,7 +12,6 @@ namespace osu.Game.Database
     public interface IHasFiles<TFile>
         where TFile : INamedFileInfo
     {
-        [NotNull]
         List<TFile> Files { get; }
 
         string Hash { get; set; }

osu.Game/Graphics/Backgrounds/BeatmapBackground.cs

@@ -22,7 +22,7 @@ namespace osu.Game.Graphics.Backgrounds
         [BackgroundDependencyLoader]
         private void load(LargeTextureStore textures)
         {
-            Sprite.Texture = Beatmap?.GetBackground() ?? textures.Get(fallbackTextureName);
+            Sprite.Texture = Beatmap.GetBackground() ?? textures.Get(fallbackTextureName);
         }
 
         public override bool Equals(Background other)

osu.Game/Graphics/ErrorTextFlowContainer.cs

@@ -23,7 +23,7 @@ namespace osu.Game.Graphics
                 RemovePart(textPart);
         }
 
-        public void AddErrors(string[] errors)
+        public void AddErrors(string[]? errors)
         {
             ClearErrors();
 

osu.Game/Graphics/UserInterface/DialogButton.cs

@@ -28,7 +28,7 @@ namespace osu.Game.Graphics.UserInterface
         private const float hover_duration = 500;
         private const float click_duration = 200;
 
-        public event Action<SelectionState> StateChanged;
+        public event Action<SelectionState>? StateChanged;
 
         private SelectionState state;
 

osu.Game/Graphics/UserInterfaceV2/OsuHSVColourPicker.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
@@ -24,7 +23,7 @@ namespace osu.Game.Graphics.UserInterfaceV2
         protected override SaturationValueSelector CreateSaturationValueSelector() => new OsuSaturationValueSelector();
 
         [BackgroundDependencyLoader(true)]
-        private void load([CanBeNull] OverlayColourProvider colourProvider, OsuColour osuColour)
+        private void load(OverlayColourProvider? colourProvider, OsuColour osuColour)
         {
             Background.Colour = colourProvider?.Dark5 ?? osuColour.GreySeaFoamDark;
 

osu.Game/Graphics/UserInterfaceV2/OsuHexColourPicker.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
@@ -21,7 +20,7 @@ namespace osu.Game.Graphics.UserInterfaceV2
         }
 
         [BackgroundDependencyLoader(true)]
-        private void load([CanBeNull] OverlayColourProvider overlayColourProvider, OsuColour osuColour)
+        private void load(OverlayColourProvider? overlayColourProvider, OsuColour osuColour)
         {
             Background.Colour = overlayColourProvider?.Dark6 ?? osuColour.GreySeaFoamDarker;
         }

osu.Game/Graphics/UserInterfaceV2/OsuPopover.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Extensions;
 using osu.Framework.Graphics;
@@ -39,7 +38,7 @@ namespace osu.Game.Graphics.UserInterfaceV2
         }
 
         [BackgroundDependencyLoader(true)]
-        private void load([CanBeNull] OverlayColourProvider colourProvider, OsuColour colours)
+        private void load(OverlayColourProvider? colourProvider, OsuColour colours)
         {
             Background.Colour = Arrow.Colour = colourProvider?.Background4 ?? colours.GreySeaFoamDarker;
         }

osu.Game/IO/OsuStorage.cs

@@ -3,7 +3,6 @@
 
 using System.Diagnostics;
 using System.Linq;
-using JetBrains.Annotations;
 using osu.Framework.Logging;
 using osu.Framework.Platform;
 using osu.Game.Configuration;
@@ -20,13 +19,11 @@ namespace osu.Game.IO
         /// <summary>
         /// The custom storage path as selected by the user.
         /// </summary>
-        [CanBeNull]
+        public string? CustomStoragePath => storageConfig.Get<string>(StorageConfig.FullPath);
-        public string CustomStoragePath => storageConfig.Get<string>(StorageConfig.FullPath);
 
         /// <summary>
         /// The default storage path to be used if a custom storage path hasn't been selected or is not accessible.
         /// </summary>
-        [NotNull]
         public string DefaultStoragePath => defaultStorage.GetFullPath(".");
 
         private readonly GameHost host;

osu.Game/Overlays/BeatmapListing/BeatmapSearchFilterRow.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
@@ -64,7 +63,6 @@ namespace osu.Game.Overlays.BeatmapListing
                 Current = filterWithValue.Current;
         }
 
-        [NotNull]
         protected virtual Drawable CreateFilter() => new BeatmapSearchFilter();
 
         protected partial class BeatmapSearchFilter : TabControl<T>

osu.Game/Overlays/BeatmapSet/Buttons/PlayButton.cs

@@ -3,6 +3,7 @@
 
 #nullable disable
 
+using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
@@ -24,6 +25,7 @@ namespace osu.Game.Overlays.BeatmapSet.Buttons
 
         private readonly BindableBool playing = new BindableBool();
 
+        [CanBeNull]
         public PreviewTrack Preview { get; private set; }
 
         private APIBeatmapSet beatmapSet;

osu.Game/Overlays/BeatmapSet/Buttons/PreviewButton.cs

@@ -20,7 +20,7 @@ namespace osu.Game.Overlays.BeatmapSet.Buttons
         private readonly Box background, progress;
         private readonly PlayButton playButton;
 
-        private PreviewTrack preview => playButton.Preview;
+        private PreviewTrack? preview => playButton.Preview;
 
         public IBindable<bool> Playing => playButton.Playing;
 

osu.Game/Overlays/Changelog/ChangelogListing.cs

@@ -16,7 +16,7 @@ namespace osu.Game.Overlays.Changelog
 {
     public partial class ChangelogListing : ChangelogContent
     {
-        private readonly List<APIChangelogBuild> entries;
+        private readonly List<APIChangelogBuild>? entries;
 
         public ChangelogListing(List<APIChangelogBuild> entries)
         {

osu.Game/Overlays/FullscreenOverlay.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Extensions.Color4Extensions;
 using osu.Framework.Graphics;
@@ -81,7 +80,6 @@ namespace osu.Game.Overlays
             Waves.FourthWaveColour = ColourProvider.Dark3;
         }
 
-        [NotNull]
         protected abstract T CreateHeader();
 
         public override void Show()

osu.Game/Overlays/OverlayHeader.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
@@ -96,10 +95,8 @@ namespace osu.Game.Overlays
             titleBackground.Colour = colourProvider.Dark5;
         }
 
-        [NotNull]
         protected virtual Drawable CreateContent() => Empty();
 
-        [NotNull]
         protected virtual Drawable CreateBackground() => Empty();
 
         protected abstract OverlayTitle CreateTitle();

osu.Game/Overlays/OverlaySidebar.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
@@ -71,7 +70,6 @@ namespace osu.Game.Overlays
             scrollbarBackground.Colour = colourProvider.Background3;
         }
 
-        [NotNull]
         protected virtual Drawable CreateContent() => Empty();
 
         private partial class SidebarScrollContainer : OsuScrollContainer

osu.Game/Overlays/Settings/Sections/DebugSettings/GeneralSettings.cs

@@ -18,7 +18,7 @@ namespace osu.Game.Overlays.Settings.Sections.DebugSettings
         protected override LocalisableString Header => DebugSettingsStrings.GeneralHeader;
 
         [BackgroundDependencyLoader(true)]
-        private void load(FrameworkDebugConfigManager config, FrameworkConfigManager frameworkConfig, IPerformFromScreenRunner performer)
+        private void load(FrameworkDebugConfigManager config, FrameworkConfigManager frameworkConfig, IPerformFromScreenRunner? performer)
         {
             Children = new Drawable[]
             {

osu.Game/Overlays/Settings/Sections/DebugSettings/MemorySettings.cs

@@ -5,6 +5,7 @@ using System;
 using System.Threading;
 using System.Threading.Tasks;
 using osu.Framework.Allocation;
+using osu.Framework.Extensions.ObjectExtensions;
 using osu.Framework.Graphics;
 using osu.Framework.Localisation;
 using osu.Framework.Logging;
@@ -56,7 +57,7 @@ namespace osu.Game.Overlays.Settings.Sections.DebugSettings
             {
                 try
                 {
-                    var token = realm.BlockAllOperations("maintenance");
+                    IDisposable? token = realm.BlockAllOperations("maintenance");
 
                     blockAction.Enabled.Value = false;
 
@@ -73,10 +74,10 @@ namespace osu.Game.Overlays.Settings.Sections.DebugSettings
 
                     void unblock()
                     {
-                        if (token == null)
+                        if (token.IsNull())
                             return;
 
-                        token?.Dispose();
+                        token.Dispose();
                         token = null;
 
                         Scheduler.Add(() =>

osu.Game/Overlays/Settings/Sections/Input/RulesetBindingsSection.cs

@@ -2,19 +2,14 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using osu.Framework.Graphics;
-using osu.Framework.Graphics.Sprites;
 using osu.Framework.Localisation;
-using osu.Game.Graphics;
 using osu.Game.Rulesets;
 
 namespace osu.Game.Overlays.Settings.Sections.Input
 {
     public partial class RulesetBindingsSection : SettingsSection
     {
-        public override Drawable CreateIcon() => ruleset?.CreateInstance().CreateIcon() ?? new SpriteIcon
+        public override Drawable CreateIcon() => ruleset.CreateInstance().CreateIcon();
-        {
-            Icon = OsuIcon.Hot
-        };
 
         public override LocalisableString Header => ruleset.Name;
 

osu.Game/Overlays/Settings/Sections/Maintenance/StableDirectorySelectScreen.cs

@@ -15,7 +15,7 @@ namespace osu.Game.Overlays.Settings.Sections.Maintenance
 
         protected override OverlayActivation InitialOverlayActivationMode => OverlayActivation.Disabled;
 
-        protected override bool IsValidDirectory(DirectoryInfo info) => info?.GetFiles("osu!.*.cfg").Any() ?? false;
+        protected override bool IsValidDirectory(DirectoryInfo? info) => info?.GetFiles("osu!.*.cfg").Any() ?? false;
 
         public override LocalisableString HeaderText => "Please select your osu!stable install location";
 

osu.Game/Overlays/Settings/SettingsFooter.cs

@@ -92,8 +92,8 @@ namespace osu.Game.Overlays.Settings
                 Height = 20;
             }
 
-            [BackgroundDependencyLoader(true)]
+            [BackgroundDependencyLoader]
-            private void load(ChangelogOverlay changelog)
+            private void load(ChangelogOverlay? changelog)
             {
                 Action = () => changelog?.ShowBuild(OsuGameBase.CLIENT_STREAM_NAME, version);
 

osu.Game/Overlays/TabControlOverlayHeader.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Extensions;
@@ -83,13 +82,11 @@ namespace osu.Game.Overlays
             controlBackground.Colour = colourProvider.Dark4;
         }
 
-        [NotNull]
         protected virtual OsuTabControl<T> CreateTabControl() => new OverlayHeaderTabControl();
 
         /// <summary>
         /// Creates a <see cref="Drawable"/> on the opposite side of the <see cref="OsuTabControl{T}"/>. Used mostly to create <see cref="OverlayRulesetSelector"/>.
         /// </summary>
-        [NotNull]
         protected virtual Drawable CreateTabControlContent() => Empty();
 
         public partial class OverlayHeaderTabControl : OverlayTabControl<T>

osu.Game/Overlays/Toolbar/ToolbarNotificationButton.cs

@@ -41,8 +41,7 @@ namespace osu.Game.Overlays.Toolbar
         {
             StateContainer = notificationOverlay as NotificationOverlay;
 
-            if (notificationOverlay != null)
+            NotificationCount.BindTo(notificationOverlay.UnreadCount);
-                NotificationCount.BindTo(notificationOverlay.UnreadCount);
 
             NotificationCount.ValueChanged += count =>
             {

osu.Game/Rulesets/Edit/Checks/CheckAudioPresence.cs

@@ -10,6 +10,6 @@ namespace osu.Game.Rulesets.Edit.Checks
     {
         protected override CheckCategory Category => CheckCategory.Audio;
         protected override string TypeOfFile => "audio";
-        protected override string? GetFilename(IBeatmap beatmap) => beatmap.Metadata?.AudioFile;
+        protected override string GetFilename(IBeatmap beatmap) => beatmap.Metadata.AudioFile;
     }
 }

osu.Game/Rulesets/Edit/Checks/CheckAudioQuality.cs

@@ -27,7 +27,7 @@ namespace osu.Game.Rulesets.Edit.Checks
 
         public IEnumerable<Issue> Run(BeatmapVerifierContext context)
         {
-            string? audioFile = context.Beatmap.Metadata?.AudioFile;
+            string audioFile = context.Beatmap.Metadata.AudioFile;
             if (string.IsNullOrEmpty(audioFile))
                 yield break;
 

osu.Game/Rulesets/Edit/Checks/CheckBackgroundPresence.cs

@@ -10,6 +10,6 @@ namespace osu.Game.Rulesets.Edit.Checks
     {
         protected override CheckCategory Category => CheckCategory.Resources;
         protected override string TypeOfFile => "background";
-        protected override string? GetFilename(IBeatmap beatmap) => beatmap.Metadata?.BackgroundFile;
+        protected override string GetFilename(IBeatmap beatmap) => beatmap.Metadata.BackgroundFile;
     }
 }

osu.Game/Rulesets/Edit/Checks/CheckBackgroundQuality.cs

@@ -33,8 +33,8 @@ namespace osu.Game.Rulesets.Edit.Checks
 
         public IEnumerable<Issue> Run(BeatmapVerifierContext context)
         {
-            string? backgroundFile = context.Beatmap.Metadata?.BackgroundFile;
+            string backgroundFile = context.Beatmap.Metadata.BackgroundFile;
-            if (backgroundFile == null)
+            if (string.IsNullOrEmpty(backgroundFile))
                 yield break;
 
             var texture = context.WorkingBeatmap.GetBackground();

osu.Game/Rulesets/Edit/DrawableEditorRulesetWrapper.cs

@@ -3,6 +3,7 @@
 
 using System.Linq;
 using osu.Framework.Allocation;
+using osu.Framework.Extensions.ObjectExtensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Game.Rulesets.Mods;
@@ -92,7 +93,7 @@ namespace osu.Game.Rulesets.Edit
         {
             base.Dispose(isDisposing);
 
-            if (beatmap != null)
+            if (beatmap.IsNotNull())
             {
                 beatmap.HitObjectAdded -= addHitObject;
                 beatmap.HitObjectRemoved -= removeHitObject;

osu.Game/Rulesets/Judgements/JudgementResult.cs

@@ -2,7 +2,6 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
-using JetBrains.Annotations;
 using osu.Game.Rulesets.Objects;
 using osu.Game.Rulesets.Objects.Drawables;
 using osu.Game.Rulesets.Scoring;
@@ -22,13 +21,11 @@ namespace osu.Game.Rulesets.Judgements
         /// <summary>
         /// The <see cref="HitObject"/> which was judged.
         /// </summary>
-        [NotNull]
         public readonly HitObject HitObject;
 
         /// <summary>
         /// The <see cref="Judgement"/> which this <see cref="JudgementResult"/> applies for.
         /// </summary>
-        [NotNull]
         public readonly Judgement Judgement;
 
         /// <summary>
@@ -97,7 +94,7 @@ namespace osu.Game.Rulesets.Judgements
         /// </summary>
         /// <param name="hitObject">The <see cref="HitObject"/> which was judged.</param>
         /// <param name="judgement">The <see cref="Judgement"/> to refer to for scoring information.</param>
-        public JudgementResult([NotNull] HitObject hitObject, [NotNull] Judgement judgement)
+        public JudgementResult(HitObject hitObject, Judgement judgement)
         {
             HitObject = hitObject;
             Judgement = judgement;

osu.Game/Rulesets/Objects/HitObjectParser.cs

@@ -5,6 +5,6 @@ namespace osu.Game.Rulesets.Objects
 {
     public abstract class HitObjectParser
     {
-        public abstract HitObject Parse(string text);
+        public abstract HitObject? Parse(string text);
     }
 }

osu.Game/Rulesets/Objects/Legacy/ConvertHitObjectParser.cs

@@ -44,7 +44,6 @@ namespace osu.Game.Rulesets.Objects.Legacy
             FormatVersion = formatVersion;
         }
 
-        [CanBeNull]
         public override HitObject Parse(string text)
         {
             string[] split = text.Split(',');

osu.Game/Rulesets/UI/IPooledHitObjectProvider.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using JetBrains.Annotations;
 using osu.Game.Rulesets.Objects;
 using osu.Game.Rulesets.Objects.Drawables;
 
@@ -15,7 +14,6 @@ namespace osu.Game.Rulesets.UI
         /// <param name="hitObject">The <see cref="HitObject"/> to retrieve the <see cref="DrawableHitObject"/> representation of.</param>
         /// <param name="parent">The parenting <see cref="DrawableHitObject"/>, if any.</param>
         /// <returns>The <see cref="DrawableHitObject"/> representing <see cref="HitObject"/>, or <c>null</c> if no poolable representation exists.</returns>
-        [CanBeNull]
+        DrawableHitObject? GetPooledDrawableRepresentation(HitObject hitObject, DrawableHitObject? parent);
-        DrawableHitObject GetPooledDrawableRepresentation([NotNull] HitObject hitObject, [CanBeNull] DrawableHitObject parent);
     }
 }

osu.Game/Scoring/Legacy/LegacyScoreEncoder.cs

@@ -126,19 +126,16 @@ namespace osu.Game.Scoring.Legacy
                 // As this is baked into hitobject timing (see `LegacyBeatmapDecoder`) we also need to apply this to replay frame timing.
                 double offset = beatmap?.BeatmapInfo.BeatmapVersion < 5 ? -LegacyBeatmapDecoder.EARLY_VERSION_TIMING_OFFSET : 0;
 
-                if (score.Replay != null)
+                int lastTime = 0;
+
+                foreach (var f in score.Replay.Frames)
                 {
-                    int lastTime = 0;
+                    var legacyFrame = getLegacyFrame(f);
 
-                    foreach (var f in score.Replay.Frames)
+                    // Rounding because stable could only parse integral values
-                    {
+                    int time = (int)Math.Round(legacyFrame.Time + offset);
-                        var legacyFrame = getLegacyFrame(f);
+                    replayData.Append(FormattableString.Invariant($"{time - lastTime}|{legacyFrame.MouseX ?? 0}|{legacyFrame.MouseY ?? 0}|{(int)legacyFrame.ButtonState},"));
-
+                    lastTime = time;
-                        // Rounding because stable could only parse integral values
-                        int time = (int)Math.Round(legacyFrame.Time + offset);
-                        replayData.Append(FormattableString.Invariant($"{time - lastTime}|{legacyFrame.MouseX ?? 0}|{legacyFrame.MouseY ?? 0}|{(int)legacyFrame.ButtonState},"));
-                        lastTime = time;
-                    }
                 }
 
                 // Warning: this is purposefully hardcoded as a string rather than interpolating, as in some cultures the minus sign is not encoded as the standard ASCII U+00C2 codepoint,

osu.Game/Screens/BackgroundScreenStack.cs

@@ -22,7 +22,7 @@ namespace osu.Game.Screens
         /// </summary>
         /// <param name="screen">The screen to attempt to push.</param>
         /// <returns>Whether the push succeeded. For example, if the existing screen was already of the correct type this will return <c>false</c>.</returns>
-        public bool Push(BackgroundScreen screen)
+        public bool Push(BackgroundScreen? screen)
         {
             if (screen == null)
                 return false;

osu.Game/Screens/Edit/Compose/Components/HitObjectOrderedSelectionContainer.cs

@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using osu.Framework.Allocation;
+using osu.Framework.Extensions.ObjectExtensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Game.Rulesets.Edit;
@@ -67,7 +68,7 @@ namespace osu.Game.Screens.Edit.Compose.Components
         {
             base.Dispose(isDisposing);
 
-            if (editorBeatmap != null)
+            if (editorBeatmap.IsNotNull())
                 editorBeatmap.BeatmapReprocessed -= SortInternal;
         }
     }

osu.Game/Screens/OnlinePlay/Multiplayer/Multiplayer.cs

@@ -3,6 +3,7 @@
 
 using System.Diagnostics;
 using osu.Framework.Allocation;
+using osu.Framework.Extensions.ObjectExtensions;
 using osu.Framework.Logging;
 using osu.Framework.Screens;
 using osu.Game.Online.Multiplayer;
@@ -93,7 +94,7 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
         {
             base.Dispose(isDisposing);
 
-            if (client != null)
+            if (client.IsNotNull())
                 client.RoomUpdated -= onRoomUpdated;
         }
     }

osu.Game/Screens/OnlinePlay/Multiplayer/Spectate/MultiSpectatorPlayerLoader.cs

@@ -2,7 +2,6 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
-using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Game.Scoring;
 using osu.Game.Screens.Menu;
@@ -15,7 +14,7 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer.Spectate
     /// </summary>
     public partial class MultiSpectatorPlayerLoader : SpectatorPlayerLoader
     {
-        public MultiSpectatorPlayerLoader([NotNull] Score score, [NotNull] Func<MultiSpectatorPlayer> createPlayer)
+        public MultiSpectatorPlayerLoader(Score score, Func<MultiSpectatorPlayer> createPlayer)
             : base(score, createPlayer)
         {
         }

osu.Game/Screens/OnlinePlay/OnlinePlaySubScreenStack.cs

@@ -1,18 +1,21 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System.Diagnostics;
 using osu.Framework.Screens;
 
 namespace osu.Game.Screens.OnlinePlay
 {
     public partial class OnlinePlaySubScreenStack : OsuScreenStack
     {
-        protected override void ScreenChanged(IScreen prev, IScreen next)
+        protected override void ScreenChanged(IScreen prev, IScreen? next)
         {
             base.ScreenChanged(prev, next);
 
             // because this is a screen stack within a screen stack, let's manually handle disabled changes to simplify things.
-            var osuScreen = ((OsuScreen)next);
+            var osuScreen = next as OsuScreen;
+
+            Debug.Assert(osuScreen != null);
 
             bool disallowChanges = osuScreen.DisallowExternalBeatmapRulesetChanges;
 

osu.Game/Screens/OsuScreenStack.cs

@@ -52,12 +52,12 @@ namespace osu.Game.Screens
             ScreenChanged(prev, next);
         }
 
-        protected virtual void ScreenChanged(IScreen prev, IScreen next)
+        protected virtual void ScreenChanged(IScreen prev, IScreen? next)
         {
             setParallax(next);
         }
 
-        private void setParallax(IScreen next) =>
+        private void setParallax(IScreen? next) =>
-            parallaxContainer.ParallaxAmount = ParallaxContainer.DEFAULT_PARALLAX_AMOUNT * (((IOsuScreen)next)?.BackgroundParallaxAmount ?? 1.0f);
+            parallaxContainer.ParallaxAmount = ParallaxContainer.DEFAULT_PARALLAX_AMOUNT * ((next as IOsuScreen)?.BackgroundParallaxAmount ?? 1.0f);
     }
 }

osu.Game/Screens/Play/HUD/HealthDisplay.cs

@@ -3,6 +3,7 @@
 
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
+using osu.Framework.Extensions.ObjectExtensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Game.Rulesets.Judgements;
@@ -59,7 +60,7 @@ namespace osu.Game.Screens.Play.HUD
         {
             base.Dispose(isDisposing);
 
-            if (HealthProcessor != null)
+            if (HealthProcessor.IsNotNull())
                 HealthProcessor.NewJudgement -= onNewJudgement;
         }
     }

osu.Game/Screens/Play/HUD/ModDisplay.cs

@@ -24,7 +24,7 @@ namespace osu.Game.Screens.Play.HUD
 
         public ExpansionMode ExpansionMode = ExpansionMode.ExpandOnHover;
 
-        private readonly BindableWithCurrent<IReadOnlyList<Mod>> current = new BindableWithCurrent<IReadOnlyList<Mod>>();
+        private readonly BindableWithCurrent<IReadOnlyList<Mod>> current = new BindableWithCurrent<IReadOnlyList<Mod>>(Array.Empty<Mod>());
 
         public Bindable<IReadOnlyList<Mod>> Current
         {
@@ -63,8 +63,6 @@ namespace osu.Game.Screens.Play.HUD
         {
             iconsContainer.Clear();
 
-            if (mods.NewValue == null) return;
-
             foreach (Mod mod in mods.NewValue)
                 iconsContainer.Add(new ModIcon(mod) { Scale = new Vector2(0.6f) });
 

osu.Game/Screens/Play/HUD/UnstableRateCounter.cs

@@ -4,6 +4,7 @@
 using System;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
+using osu.Framework.Extensions.ObjectExtensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Sprites;
@@ -75,10 +76,11 @@ namespace osu.Game.Screens.Play.HUD
         {
             base.Dispose(isDisposing);
 
-            if (scoreProcessor == null) return;
+            if (scoreProcessor.IsNotNull())
-
+            {
-            scoreProcessor.NewJudgement -= updateDisplay;
+                scoreProcessor.NewJudgement -= updateDisplay;
-            scoreProcessor.JudgementReverted -= updateDisplay;
+                scoreProcessor.JudgementReverted -= updateDisplay;
+            }
         }
 
         private partial class TextComponent : CompositeDrawable, IHasText

osu.Game/Screens/Play/SpectatorResultsScreen.cs

@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using osu.Framework.Allocation;
+using osu.Framework.Extensions.ObjectExtensions;
 using osu.Framework.Screens;
 using osu.Game.Online.Spectator;
 using osu.Game.Scoring;
@@ -40,7 +41,7 @@ namespace osu.Game.Screens.Play
         {
             base.Dispose(isDisposing);
 
-            if (spectatorClient != null)
+            if (spectatorClient.IsNotNull())
                 spectatorClient.OnUserBeganPlaying -= userBeganPlaying;
         }
     }

osu.Game/Screens/Ranking/Statistics/StatisticContainer.cs

@@ -1,7 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using System.Diagnostics.CodeAnalysis;
 using osu.Framework.Extensions.Color4Extensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
@@ -22,7 +21,7 @@ namespace osu.Game.Screens.Ranking.Statistics
         /// Creates a new <see cref="StatisticContainer"/>.
         /// </summary>
         /// <param name="item">The <see cref="StatisticItem"/> to display.</param>
-        public StatisticContainer([NotNull] StatisticItem item)
+        public StatisticContainer(StatisticItem item)
         {
             RelativeSizeAxes = Axes.X;
             AutoSizeAxes = Axes.Y;

osu.Game/Screens/Ranking/Statistics/StatisticItem.cs

@@ -2,7 +2,6 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
-using JetBrains.Annotations;
 using osu.Framework.Graphics;
 using osu.Framework.Localisation;
 
@@ -34,7 +33,7 @@ namespace osu.Game.Screens.Ranking.Statistics
         /// <param name="name">The name of the item. Can be <see langword="null"/> to hide the item header.</param>
         /// <param name="createContent">A function returning the <see cref="Drawable"/> content to be displayed.</param>
         /// <param name="requiresHitEvents">Whether this item requires hit events. If true, <see cref="CreateContent"/> will not be called if no hit events are available.</param>
-        public StatisticItem(LocalisableString name, [NotNull] Func<Drawable> createContent, bool requiresHitEvents = false)
+        public StatisticItem(LocalisableString name, Func<Drawable> createContent, bool requiresHitEvents = false)
         {
             Name = name;
             RequiresHitEvents = requiresHitEvents;

osu.Game/Storyboards/Drawables/DrawableStoryboardSprite.cs

@@ -3,6 +3,7 @@
 
 using System;
 using osu.Framework.Allocation;
+using osu.Framework.Extensions.ObjectExtensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Sprites;
 using osu.Framework.Graphics.Textures;
@@ -106,7 +107,7 @@ namespace osu.Game.Storyboards.Drawables
         {
             base.Dispose(isDisposing);
 
-            if (skin != null)
+            if (skin.IsNotNull())
                 skin.SourceChanged -= skinSourceChanged;
         }
     }