PaperMC/Spigot-Server-Patches/0449-Don-t-crash-if-player-is-attempted-to-be-removed-fro.patch

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 706ef10959df897a4b1889c2e2e7ff41ed924876..52a69edcefb72a3908ecd522ef87e7eb989467a6 100644
--- a/src/main/java/net/minecraft/server/ChunkMapDistance.java
+++ b/src/main/java/net/minecraft/server/ChunkMapDistance.java
@@ -239,8 +239,8 @@ public abstract class ChunkMapDistance {
         ObjectSet<EntityPlayer> objectset = (ObjectSet) this.c.get(i);
         if (objectset == null) return; // CraftBukkit - SPIGOT-6208
 
-        objectset.remove(entityplayer);
-        if (objectset.isEmpty()) {
+        if (objectset != null) objectset.remove(entityplayer); // Paper - some state corruption happens here, don't crash, clean up gracefully.
+        if (objectset == null || objectset.isEmpty()) { // Paper
             this.c.remove(i);
             this.f.update(i, Integer.MAX_VALUE, false);
             this.g.update(i, Integer.MAX_VALUE, false);