From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sat, 18 Apr 2020 15:59:41 -0400
Subject: [PATCH] Don't crash if player is attempted to be removed from
 untracked chunk.

I suspect it deals with teleporting as it uses players current x/y/z

diff --git a/src/main/java/net/minecraft/server/ChunkMapDistance.java b/src/main/java/net/minecraft/server/ChunkMapDistance.java
index 83da76fdc495225b563cecbdb71422aec2b534f3..4e0ea454f00c69f03023f01c1d4bd2eda5553a02 100644
--- a/src/main/java/net/minecraft/server/ChunkMapDistance.java
+++ b/src/main/java/net/minecraft/server/ChunkMapDistance.java
@@ -237,6 +237,7 @@ public abstract class ChunkMapDistance {
     public void b(SectionPosition sectionposition, EntityPlayer entityplayer) {
         long i = sectionposition.u().pair();
         ObjectSet<EntityPlayer> objectset = (ObjectSet) this.c.get(i);
+        if (objectset == null) return; // Paper - mitigate weird state mismatch that this chunk isn't tracked.
 
         objectset.remove(entityplayer);
         if (objectset.isEmpty()) {