Enable NRT in explosion-related classes and streamline null handling

osu.Game.Rulesets.Catch/Skinning/Default/DefaultHitExplosion.cs

@@ -72,9 +72,6 @@ namespace osu.Game.Rulesets.Catch.Skinning.Default
 
         public void Animate(HitExplosionEntry entry)
         {
-            if (entry == null)
-                return;
-
             X = entry.Position;
             Scale = new Vector2(entry.HitObject.Scale);
             setColour(entry.ObjectColour);

osu.Game.Rulesets.Catch/Skinning/Legacy/LegacyHitExplosion.cs

@@ -62,9 +62,6 @@ namespace osu.Game.Rulesets.Catch.Skinning.Legacy
 
         public void Animate(HitExplosionEntry entry)
         {
-            if (entry == null)
-                return;
-
             Colour = entry.ObjectColour;
 
             using (BeginAbsoluteSequence(entry.LifetimeStart))

osu.Game.Rulesets.Catch/UI/HitExplosion.cs

@@ -1,28 +1,25 @@
 // 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 osu.Framework.Allocation;
 using osu.Framework.Graphics;
 using osu.Game.Rulesets.Catch.Skinning.Default;
 using osu.Game.Rulesets.Objects.Pooling;
 using osu.Game.Skinning;
 
+#nullable enable
+
 namespace osu.Game.Rulesets.Catch.UI
 {
     public class HitExplosion : PoolableDrawableWithLifetime<HitExplosionEntry>
     {
-        private SkinnableDrawable skinnableExplosion;
+        private readonly SkinnableDrawable skinnableExplosion;
 
         public HitExplosion()
         {
             RelativeSizeAxes = Axes.Both;
             Anchor = Anchor.BottomCentre;
             Origin = Anchor.BottomCentre;
-        }
 
-        [BackgroundDependencyLoader]
-        private void load()
-        {
             InternalChild = skinnableExplosion = new SkinnableDrawable(new CatchSkinComponent(CatchSkinComponents.HitExplosion), _ => new DefaultHitExplosion())
             {
                 CentreComponent = false,
@@ -44,8 +41,11 @@ namespace osu.Game.Rulesets.Catch.UI
             apply(Entry);
         }
 
-        private void apply(HitExplosionEntry entry)
+        private void apply(HitExplosionEntry? entry)
         {
+            if (entry == null)
+                return;
+
             ApplyTransformsAt(double.MinValue, true);
             ClearTransforms(true);
 

osu.Game.Rulesets.Catch/UI/HitExplosionEntry.cs

@@ -6,6 +6,8 @@ using osu.Game.Rulesets.Catch.Objects;
 using osu.Game.Rulesets.Judgements;
 using osuTK.Graphics;
 
+#nullable enable
+
 namespace osu.Game.Rulesets.Catch.UI
 {
     public class HitExplosionEntry : LifetimeEntry

osu.Game.Rulesets.Catch/UI/IHitExplosion.cs

@@ -1,6 +1,8 @@
 // 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.
 
+#nullable enable
+
 namespace osu.Game.Rulesets.Catch.UI
 {
     /// <summary>