The issue is that using PlayerPortalEvent.setTo() when returning from The End causes the server to crash. At first I thought that this was caused by MV setting the Location to one with a null world, however, that turned out not to be the case (I fixed said issue and the server still crashed).

Steps to reproduce:
1. Setup Spigot Server.
2. Install MV Core and NetherPorals (the uploaded versions).
3. Create two new worlds: (/mvc test normal) and (/mvc test_the_end end).
4. Create an End Portal in the "test" World and jump in.
5. Defeat the Ender Dragon (have fun I guess... ).
6. Jump into the exit portal.

I've used the IJ Debugger and I doubt there is anything wrong with MV since the Location returned is valid (with the versions I uploaded). I've also attached the Server and Crash Logs.