Use empty hitwindows instead of null

osu.Game.Rulesets.Catch/Objects/CatchHitObject.cs

@@ -93,7 +93,7 @@ namespace osu.Game.Rulesets.Catch.Objects
             Scale = 1.0f - 0.7f * (difficulty.CircleSize - 5) / 5;
         }
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 
     public enum FruitVisualRepresentation

osu.Game.Rulesets.Mania/Objects/HoldNote.cs

@@ -101,6 +101,6 @@ namespace osu.Game.Rulesets.Mania.Objects
 
         public override Judgement CreateJudgement() => new HoldNoteJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game.Rulesets.Mania/Objects/HoldNoteTick.cs

@@ -14,6 +14,6 @@ namespace osu.Game.Rulesets.Mania.Objects
     {
         public override Judgement CreateJudgement() => new HoldNoteTickJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game.Rulesets.Osu/Objects/RepeatPoint.cs

@@ -30,6 +30,6 @@ namespace osu.Game.Rulesets.Osu.Objects
 
         public override Judgement CreateJudgement() => new OsuJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game.Rulesets.Osu/Objects/Slider.cs

@@ -205,6 +205,6 @@ namespace osu.Game.Rulesets.Osu.Objects
 
         public override Judgement CreateJudgement() => new OsuJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game.Rulesets.Osu/Objects/SliderTailCircle.cs

@@ -25,6 +25,6 @@ namespace osu.Game.Rulesets.Osu.Objects
 
         public override Judgement CreateJudgement() => new OsuSliderTailJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game.Rulesets.Osu/Objects/SliderTick.cs

@@ -32,6 +32,6 @@ namespace osu.Game.Rulesets.Osu.Objects
 
         public override Judgement CreateJudgement() => new OsuJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game.Rulesets.Osu/Objects/Spinner.cs

@@ -33,6 +33,6 @@ namespace osu.Game.Rulesets.Osu.Objects
 
         public override Judgement CreateJudgement() => new OsuJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game.Rulesets.Taiko/Objects/DrumRoll.cs

@@ -88,6 +88,6 @@ namespace osu.Game.Rulesets.Taiko.Objects
 
         public override Judgement CreateJudgement() => new TaikoDrumRollJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game.Rulesets.Taiko/Objects/DrumRollTick.cs

@@ -27,6 +27,6 @@ namespace osu.Game.Rulesets.Taiko.Objects
 
         public override Judgement CreateJudgement() => new TaikoDrumRollTickJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game.Rulesets.Taiko/Objects/StrongHitObject.cs

@@ -11,6 +11,6 @@ namespace osu.Game.Rulesets.Taiko.Objects
     {
         public override Judgement CreateJudgement() => new TaikoStrongJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game.Rulesets.Taiko/Objects/Swell.cs

@@ -35,6 +35,6 @@ namespace osu.Game.Rulesets.Taiko.Objects
 
         public override Judgement CreateJudgement() => new TaikoSwellJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game.Rulesets.Taiko/Objects/SwellTick.cs

@@ -11,6 +11,6 @@ namespace osu.Game.Rulesets.Taiko.Objects
     {
         public override Judgement CreateJudgement() => new TaikoSwellTickJudgement();
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game/Rulesets/Objects/HitObject.cs

@@ -66,7 +66,6 @@ namespace osu.Game.Rulesets.Objects
         /// <summary>
         /// The hit windows for this <see cref="HitObject"/>.
         /// </summary>
-        [CanBeNull]
         public HitWindows HitWindows { get; set; }
 
         private readonly List<HitObject> nestedHitObjects = new List<HitObject>();
@@ -113,10 +112,7 @@ namespace osu.Game.Rulesets.Objects
             nestedHitObjects.Sort((h1, h2) => h1.StartTime.CompareTo(h2.StartTime));
 
             foreach (var h in nestedHitObjects)
-            {
-                h.HitWindows = HitWindows;
                 h.ApplyDefaults(controlPointInfo, difficulty);
-            }
         }
 
         protected virtual void ApplyDefaultsToSelf(ControlPointInfo controlPointInfo, BeatmapDifficulty difficulty)
@@ -147,7 +143,7 @@ namespace osu.Game.Rulesets.Objects
         /// This will only be invoked if <see cref="HitWindows"/> hasn't been set externally (e.g. from a <see cref="BeatmapConverter{T}"/>.
         /// </para>
         /// </summary>
-        [CanBeNull]
+        [NotNull]
         protected virtual HitWindows CreateHitWindows() => new HitWindows();
     }
 }

osu.Game/Rulesets/Objects/Legacy/Mania/ConvertHit.cs

@@ -13,6 +13,6 @@ namespace osu.Game.Rulesets.Objects.Legacy.Mania
     {
         public float X { get; set; }
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game/Rulesets/Objects/Legacy/Mania/ConvertHold.cs

@@ -14,6 +14,6 @@ namespace osu.Game.Rulesets.Objects.Legacy.Mania
 
         public double Duration => EndTime - StartTime;
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game/Rulesets/Objects/Legacy/Mania/ConvertSlider.cs

@@ -13,6 +13,6 @@ namespace osu.Game.Rulesets.Objects.Legacy.Mania
     {
         public float X { get; set; }
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game/Rulesets/Objects/Legacy/Mania/ConvertSpinner.cs

@@ -17,6 +17,6 @@ namespace osu.Game.Rulesets.Objects.Legacy.Mania
 
         public float X { get; set; }
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game/Rulesets/Objects/Legacy/Osu/ConvertHit.cs

@@ -22,6 +22,6 @@ namespace osu.Game.Rulesets.Objects.Legacy.Osu
 
         public int ComboOffset { get; set; }
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game/Rulesets/Objects/Legacy/Osu/ConvertSlider.cs

@@ -22,6 +22,6 @@ namespace osu.Game.Rulesets.Objects.Legacy.Osu
 
         public int ComboOffset { get; set; }
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game/Rulesets/Objects/Legacy/Osu/ConvertSpinner.cs

@@ -22,7 +22,7 @@ namespace osu.Game.Rulesets.Objects.Legacy.Osu
 
         public float Y => Position.Y;
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
 
         public bool NewCombo { get; set; }
 

osu.Game/Rulesets/Objects/Legacy/Taiko/ConvertHit.cs

@@ -10,6 +10,6 @@ namespace osu.Game.Rulesets.Objects.Legacy.Taiko
     /// </summary>
     internal sealed class ConvertHit : HitObject
     {
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game/Rulesets/Objects/Legacy/Taiko/ConvertSlider.cs

@@ -10,6 +10,6 @@ namespace osu.Game.Rulesets.Objects.Legacy.Taiko
     /// </summary>
     internal sealed class ConvertSlider : Legacy.ConvertSlider
     {
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game/Rulesets/Objects/Legacy/Taiko/ConvertSpinner.cs

@@ -15,6 +15,6 @@ namespace osu.Game.Rulesets.Objects.Legacy.Taiko
 
         public double Duration => EndTime - StartTime;
 
-        protected override HitWindows CreateHitWindows() => null;
+        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
     }
 }

osu.Game/Rulesets/Scoring/HitWindows.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using osu.Game.Beatmaps;
 using osu.Game.Rulesets.Objects;
 
@@ -30,6 +31,17 @@ namespace osu.Game.Rulesets.Scoring
         private double meh;
         private double miss;
 
+        /// <summary>
+        /// An empty <see cref="HitWindows"/> with only <see cref="HitResult.Miss"/> and <see cref="HitResult.Perfect"/>.
+        /// No time values are provided (meaning instantaneous hit or miss).
+        /// </summary>
+        public static HitWindows Empty => new EmptyHitWindows();
+
+        public HitWindows()
+        {
+            Debug.Assert(GetRanges().Length >= 1, $"{nameof(HitWindows)}");
+        }
+
         /// <summary>
         /// Retrieves the <see cref="HitResult"/> with the largest hit window that produces a successful hit.
         /// </summary>
@@ -168,6 +180,29 @@ namespace osu.Game.Rulesets.Scoring
         /// Defaults are provided but can be overridden to customise for a ruleset.
         /// </summary>
         protected virtual DifficultyRange[] GetRanges() => base_ranges;
+
+        public class EmptyHitWindows : HitWindows
+        {
+            private static readonly DifficultyRange[] ranges =
+            {
+                new DifficultyRange(HitResult.Perfect, 0, 0, 0),
+                new DifficultyRange(HitResult.Miss, 0, 0, 0),
+            };
+
+            public override bool IsHitResultAllowed(HitResult result)
+            {
+                switch (result)
+                {
+                    case HitResult.Great:
+                    case HitResult.Miss:
+                        return true;
+                }
+
+                return false;
+            }
+
+            protected override DifficultyRange[] GetRanges() => ranges;
+        }
     }
 
     public struct DifficultyRange

osu.Game/Rulesets/UI/DrawableRuleset.cs

@@ -426,11 +426,11 @@ namespace osu.Game.Rulesets.UI
             {
                 foreach (var h in Objects)
                 {
-                    if (h.HitWindows != null)
+                    if (h.HitWindows.WindowFor(HitResult.Miss) > 0)
                         return h.HitWindows;
 
                     foreach (var n in h.NestedHitObjects)
-                        if (n.HitWindows != null)
+                        if (h.HitWindows.WindowFor(HitResult.Miss) > 0)
                             return n.HitWindows;
                 }
 

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

@@ -48,7 +48,7 @@ namespace osu.Game.Screens.Play.HUD
 
         private void onNewJudgement(JudgementResult result)
         {
-            if (result.HitObject.HitWindows == null)
+            if (result.HitObject.HitWindows.WindowFor(HitResult.Miss) == 0)
                 return;
 
             foreach (var c in Children)