Nullpointer thrown when entering end portal to the overworld

When in the end dimension, The enderdragon has been defeated, Entering the portal back back to the overworld causes the server throw a Nullpointer exception, the server does however not crash, only throwing an error in the console.

```

[Server thread/FATAL]: Error executing task on Server
java.lang.NullPointerException: null
at yk.b(SourceFile:201) ~[server.jar:?]
at yd.a(SourceFile:939) ~[server.jar:?]
at yp.a(SourceFile:479) ~[server.jar:?]
at zj.a(SourceFile:860) ~[server.jar:?]
at ro.a(SourceFile:122) ~[server.jar:?]
at ro$a.a(SourceFile:56) ~[server.jar:?]
at nf.a(SourceFile:21) ~[server.jar:?]
at um.run(SourceFile:18) ~[server.jar:?]
at alp.c(SourceFile:144) [server.jar:?]
at alt.c(SourceFile:23) [server.jar:?]
at net.minecraft.server.MinecraftServer.b(SourceFile:716) [server.jar:?]
at net.minecraft.server.MinecraftServer.c(SourceFile:149) [server.jar:?]
at alp.w(SourceFile:118) [server.jar:?]
at net.minecraft.server.MinecraftServer.bb(SourceFile:698) [server.jar:?]
at net.minecraft.server.MinecraftServer.w(SourceFile:692) [server.jar:?]
at alp.bk(SourceFile:103) [server.jar:?]
at net.minecraft.server.MinecraftServer.v(SourceFile:676) [server.jar:?]
at net.minecraft.server.MinecraftServer.run(SourceFile:629) [server.jar:?]
at java.lang.Thread.run(Thread.java:834) [?:?]

```