[ci skip] Add nullable annotation to field (#7042)

Co-authored-by: Riley Park <rileysebastianpark@gmail.com>

patches/server/Add-Debug-Entities-option-to-debug-dupe-uuid-issues.patch

@@ -79,7 +79,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      public com.destroystokyo.paper.loottable.PaperLootableInventoryData lootableData; // Paper
      private CraftEntity bukkitEntity;
  
-+    public net.minecraft.server.level.ChunkMap.TrackedEntity tracker; // Paper
++    public @org.jetbrains.annotations.Nullable net.minecraft.server.level.ChunkMap.TrackedEntity tracker; // Paper
 +    public Throwable addedToWorldStack; // Paper - entity debug
      public CraftEntity getBukkitEntity() {
          if (this.bukkitEntity == null) {

patches/server/Optimize-Collision-to-not-load-chunks.patch

@@ -36,7 +36,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    public boolean collisionLoadChunks = false; // Paper
      private CraftEntity bukkitEntity;
  
-     public net.minecraft.server.level.ChunkMap.TrackedEntity tracker; // Paper
+     public @org.jetbrains.annotations.Nullable net.minecraft.server.level.ChunkMap.TrackedEntity tracker; // Paper
 diff --git a/src/main/java/net/minecraft/world/level/BlockCollisions.java b/src/main/java/net/minecraft/world/level/BlockCollisions.java
 index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
 --- a/src/main/java/net/minecraft/world/level/BlockCollisions.java