Not working the respawn

[Rubli98]

Can you help me?
[Server thread/ERROR]: Could not pass event CreatureSpawnEvent to EnderDragon v2.5.4
java.lang.NullPointerException: Cannot invoke "java.util.List.iterator()" because "pers.xanadu.enderdragon.manager.DragonManager.dragons" is null
at EnderDragon-2.5.4.jar/pers.xanadu.enderdragon.manager.DragonManager.getDesignatedDragon(DragonManager.java:621) ~[EnderDragon-2.5.4.jar:?]
at EnderDragon-2.5.4.jar/pers.xanadu.enderdragon.listener.DragonSpawnListener.OnDragonSpawn(DragonSpawnListener.java:47) ~[EnderDragon-2.5.4.jar:?]

[Server thread/ERROR]: Could not pass event EntityRegainHealthEvent to EnderDragon v2.5.4
java.lang.NullPointerException: Cannot invoke "java.util.List.iterator()" because "pers.xanadu.enderdragon.manager.DragonManager.dragons" is null
at EnderDragon-2.5.4.jar/pers.xanadu.enderdragon.manager.DragonManager.getSpecialKey(DragonManager.java:140) ~[EnderDragon-2.5.4.jar:?]
at EnderDragon-2.5.4.jar/pers.xanadu.enderdragon.listener.DragonHealListener.OnDragonHeal(DragonHealListener.java:21) ~[EnderDragon-2.5.4.jar:?]

[iXanadu13]

when did this error occur? Soon after the server started, or soon after “ed reload”?
It seems that one static field(named dragons) hasn't been initialized.

[Rubli98]

The error occurs when we use endcrystals to respawn a dragon, A dragon spawn but its a normal dragon. The second error occurs when the dragon touch us.

[iXanadu13]

Is there are any errors when starting the server?Or try to execute /ed reload and see if any errors report.

[Rubli98]

[07:20:28] [Craft Scheduler Thread - 1 - EnderDragon/INFO]: [EnderDragon] You are using the latest version (v2.5.4)...
[07:20:34] [Server thread/WARN]: [EnderDragon] Task #21 for EnderDragon v2.5.4 generated an exception
java.lang.UnsupportedOperationException: null
at java.base/java.util.AbstractList.add(Unknown Source) ~[?:?]
at java.base/java.util.AbstractList.add(Unknown Source) ~[?:?]
at EnderDragon-2.5.4.jar/pers.xanadu.enderdragon.manager.DragonManager.lambda$readSettingFile$4(DragonManager.java:311) ~[EnderDragon-2.5.4.jar:?]
at java.base/java.util.HashMap.compute(Unknown Source) ~[?:?]
at EnderDragon-2.5.4.jar/pers.xanadu.enderdragon.manager.DragonManager.readSettingFile(DragonManager.java:309) ~[EnderDragon-2.5.4.jar:?]
at EnderDragon-2.5.4.jar/pers.xanadu.enderdragon.manager.DragonManager.reload(DragonManager.java:103) ~[EnderDragon-2.5.4.jar:?]
at EnderDragon-2.5.4.jar/pers.xanadu.enderdragon.EnderDragon$2.run(EnderDragon.java:130) ~[EnderDragon-2.5.4.jar:?]
at org.bukkit.craftbukkit.scheduler.CraftTask.run(CraftTask.java:86) ~[paper-1.21.1.jar:1.21.1-131-84281ce]
at org.bukkit.craftbukkit.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:475) ~[paper-1.21.1.jar:1.21.1-131-84281ce]
at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1225) ~[paper-1.21.1.jar:1.21.1-131-84281ce]
at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:329) ~[paper-1.21.1.jar:1.21.1-131-84281ce]
at java.base/java.lang.Thread.run(Unknown Source) ~[?:?]

[iXanadu13]

What about your server type and version?

[Rubli98]

Paper 1.21.1

[iXanadu13]

I know what went wrong and I will fix it soon.