From 86e26e7c235ffbd1dc52242b42c40ff55bef6b4c 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 0244768f7..279c7a85f 100644
--- a/src/main/java/net/minecraft/server/ChunkMapDistance.java
+++ b/src/main/java/net/minecraft/server/ChunkMapDistance.java
@@ -226,6 +226,7 @@ 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()) {
-- 
2.25.1