Plugin runs perfectly when starting the server , but when player enter , it throw this exception

[16:57:42] [Server thread/WARN]: [BagOfGold] Task #3365 for BagOfGold v2.6.8 generated an exception java.util.NoSuchElementException: null at com.google.common.collect.LinkedHashMultimap$ValueSet$1.next(LinkedHashMultimap.java:403) ~[spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at com.google.common.collect.AbstractMapBasedMultimap$WrappedCollection$WrappedIterator.next(AbstractMapBasedMultimap.java:496) ~[spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at one.lindegaard.Core.skins.Skins_1_13_R2.getSkin(Skins_1_13_R2.java:20) ~[?:?] at one.lindegaard.BagOfGold.rewards.CustomItems.getPlayerHead(CustomItems.java:129) ~[?:?] at one.lindegaard.BagOfGold.PlayerSettingsManager$1.onCompleted(PlayerSettingsManager.java:122) ~[?:?] at one.lindegaard.BagOfGold.PlayerSettingsManager$1.onCompleted(PlayerSettingsManager.java:113) ~[?:?] at one.lindegaard.BagOfGold.storage.DataStoreManager$CallbackCaller.run(DataStoreManager.java:234) ~[?:?] at org.bukkit.craftbukkit.v1_13_R2.scheduler.CraftTask.run(CraftTask.java:81) ~[spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at org.bukkit.craftbukkit.v1_13_R2.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:392) [spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at net.minecraft.server.v1_13_R2.MinecraftServer.b(MinecraftServer.java:889) [spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at net.minecraft.server.v1_13_R2.DedicatedServer.b(DedicatedServer.java:417) [spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at net.minecraft.server.v1_13_R2.MinecraftServer.a(MinecraftServer.java:831) [spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at net.minecraft.server.v1_13_R2.MinecraftServer.run(MinecraftServer.java:729) [spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at java.lang.Thread.run(Unknown Source) [?:1.8.0_211] [16:57:42] [Server thread/WARN]: [MobHunting] Task #3392 for MobHunting v6.7.4 generated an exception java.util.NoSuchElementException: null at com.google.common.collect.LinkedHashMultimap$ValueSet$1.next(LinkedHashMultimap.java:403) ~[spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at com.google.common.collect.AbstractMapBasedMultimap$WrappedCollection$WrappedIterator.next(AbstractMapBasedMultimap.java:496) ~[spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at one.lindegaard.Core.skins.Skins_1_13_R2.getSkin(Skins_1_13_R2.java:20) ~[?:?] at one.lindegaard.MobHunting.rewards.CustomItems.getPlayerHead(CustomItems.java:121) ~[?:?] at one.lindegaard.MobHunting.PlayerSettingsManager$1.onCompleted(PlayerSettingsManager.java:125) ~[?:?] at one.lindegaard.MobHunting.PlayerSettingsManager$1.onCompleted(PlayerSettingsManager.java:112) ~[?:?] at one.lindegaard.MobHunting.storage.DataStoreManager$CallbackCaller.run(DataStoreManager.java:341) ~[?:?] at org.bukkit.craftbukkit.v1_13_R2.scheduler.CraftTask.run(CraftTask.java:81) ~[spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at org.bukkit.craftbukkit.v1_13_R2.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:392) [spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at net.minecraft.server.v1_13_R2.MinecraftServer.b(MinecraftServer.java:889) [spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at net.minecraft.server.v1_13_R2.DedicatedServer.b(DedicatedServer.java:417) [spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at net.minecraft.server.v1_13_R2.MinecraftServer.a(MinecraftServer.java:831) [spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at net.minecraft.server.v1_13_R2.MinecraftServer.run(MinecraftServer.java:729) [spigot-1.13.2.jar:git-Spigot-1a3504a-84f3da3] at java.lang.Thread.run(Unknown Source) [?:1.8.0_211]
I m from china , it is a excellent plugin ! thanks for your hard working !

Im not able reproduce this bug, but I think I have made a fix. Can you please help me with the testing. Please test this build:

https://fractal.lindegaard.one:8181/job/BagOfGold/281/

And let me know if it works?

it works perfectly ! Thanks for your reply ! You and these plugins are quite awesome !
And sry for my late replay

I delete the plugin folder and restart to generate a new one , then when a player enter in it shows me that[BagOfGold]�[m mTranslationTable has not key: bagofgold.reward.name�[m
idk if it is a bug

Its not a bug, its just telling you that a key has been created because it was missing. You will get a similar lot of warnings, if you install a third party mob plugin like MythicMobs and smilar.