When calling DragonBattle#getEndPortalLocation() on a world where the dragon has not yet been summoned, the following NullPointerException is generated:

25.06 16:33:08 [Server] INFO java.lang.NullPointerException: null
25.06 16:33:08 [Server] INFO at org.bukkit.craftbukkit.v1_16_R1.boss.CraftDragonBattle.getEndPortalLocation(CraftDragonBattle.java:33) ~[spigot-1.16.1.jar:git-Spigot-6f4ff1b-71045d3]

I believe this is as a result of 1.15.2 worlds being converted to 1.16.1 worlds incorrectly whereby dragon information is not stored properly.

I will be creating a PR to address this issue shortly