EDIT: A player entered the end and flew straight away
[15:15:50] [Server thread/INFO]: <PlayerName> fell out of the world
[15:15:51] [Server thread/FATAL]: Error executing task on Server
java.lang.NullPointerException: Cannot invoke "it.unimi.dsi.fastutil.objects.ObjectSet.remove(Object)" because "☃" is null
at net.minecraft.class_3204.method_14051(class_3204.java:202) ~[intermediary-server.jar:?]
at net.minecraft.class_3898.method_18713(class_3898.java:2218) ~[intermediary-server.jar:?]
at net.minecraft.class_3215.method_14096(class_3215.java:450) ~[intermediary-server.jar:?]
at net.minecraft.class_3244.method_12063(class_3244.java:927) ~[intermediary-server.jar:?]
at net.minecraft.class_2828.method_12272(class_2828.java:114) ~[intermediary-server.jar:?]
at net.minecraft.class_2828$class_2829.method_11054(class_2828.java:42) ~[intermediary-server.jar:?]
at net.minecraft.class_2600.method_11072(class_2600.java:21) ~[intermediary-server.jar:?]
at net.minecraft.class_3738.run(class_3738.java:18) ~[intermediary-server.jar:?]
at net.minecraft.class_1255.method_18859(class_1255.java:151) ~[intermediary-server.jar:?]
at net.minecraft.class_4093.method_18859(class_4093.java:23) ~[intermediary-server.jar:?]
at net.minecraft.server.MinecraftServer.method_24306(MinecraftServer.java:788) ~[intermediary-server.jar:?]
at net.minecraft.server.MinecraftServer.method_18859(MinecraftServer.java:164) ~[intermediary-server.jar:?]
at net.minecraft.class_1255.method_16075(class_1255.java:125) ~[intermediary-server.jar:?]
at net.minecraft.server.MinecraftServer.method_20415(MinecraftServer.java:770) ~[intermediary-server.jar:?]
at net.minecraft.server.MinecraftServer.method_16075(MinecraftServer.java:764) ~[intermediary-server.jar:?]
at net.minecraft.class_1255.method_5383(class_1255.java:110) ~[intermediary-server.jar:?]
at net.minecraft.server.MinecraftServer.method_16208(MinecraftServer.java:748) ~[intermediary-server.jar:?]
at net.minecraft.server.MinecraftServer.method_29741(MinecraftServer.java:701) ~[intermediary-server.jar:?]
at net.minecraft.server.MinecraftServer.method_29739(MinecraftServer.java:270) ~[intermediary-server.jar:?]
at java.lang.Thread.run(Thread.java:831) [?:?]
EDIT: A player entered the end and flew straight away