When you spawn in a ender dragon, after a while mc crashes and it says

Error: java.lang.NullPointerException: Cannot invoke "net.minecraft.world.level.dimension.end.EndDragonFight.m_64098_()" because the return value of "net.minecraft.world.entity.boss.enderdragon.EnderDragon.m_31158_()" is null

what does this mean and how do you fix it?
version: epicfight-18.1.18 beta jar

The ender dragon is programmed for the end. If he gets spawned some where else the game will crash and there's nothing we can do about it.

Full crash report please