Problem/Bug EssentialsX, /nick returns an error.

I was attempting to use /nick for myself as people call me that usually
I was planning to use
/nick Calorious &5&lJava
(&5 -> Purple)
(&l -> Bold)

But it returned me an error.
At the start of the server, I have a message that says

Console Startup Version mismatch.

4Version mismatch! Please update EssentialsChat to the same version.
[20:51:28 WARN]: [Essentials] º4Version mismatch! Please update EssentialsSpawn to the same version.

but I don't think thats the problem with being unable to use /nick right?
(You may use #1: (Your answer) to tell me whether thats the problem.)

Error when using /nick (open) Error when using /nick (close)

Error calling the command /nick
java.lang.NullPointerException
at net.milkbowl.vault.chat.plugins.Chat_GroupManager.getPlayerPrefix(Chat_GroupManager.java:275) ~[Vault.jar:?]
at net.milkbowl.vault.chat.Chat.getPlayerPrefix(Chat.java:67) ~[Vault.jar:?]
at net.milkbowl.vault.chat.Chat.getPlayerPrefix(Chat.java:91) ~[Vault.jar:?]
at com.earth2me.essentials.perm.impl.AbstractVaultHandler.getPrefix(AbstractVaultHandler.java:48) ~[EssentialsX-2.0.1.jar:?]
at com.earth2me.essentials.perm.PermissionsHandler.getPrefix(PermissionsHandler.java:68) ~[EssentialsX-2.0.1.jar:?]
at com.earth2me.essentials.User.getNick(User.java:310) ~[EssentialsX-2.0.1.jar:?]
at com.earth2me.essentials.User.getNick(User.java:279) ~[EssentialsX-2.0.1.jar:?]
at com.earth2me.essentials.User.setDisplayNick(User.java:339) ~[EssentialsX-2.0.1.jar:?]
at com.earth2me.essentials.commands.Commandnick.setNickname(Commandnick.java:114) ~[EssentialsX-2.0.1.jar:?]
at com.earth2me.essentials.commands.Commandnick.updatePlayer(Commandnick.java:71) ~[EssentialsX-2.0.1.jar:?]
at com.earth2me.essentials.commands.EssentialsLoopCommand.loopOfflinePlayers(EssentialsLoopCommand.java:54) ~[EssentialsX-2.0.1.jar:?]
at com.earth2me.essentials.commands.Commandnick.run(Commandnick.java:51) ~[EssentialsX-2.0.1.jar:?]
at com.earth2me.essentials.commands.EssentialsCommand.run(EssentialsCommand.java:167) ~[EssentialsX-2.0.1.jar:?]
at com.earth2me.essentials.Essentials.onCommandEssentials(Essentials.java:512) [EssentialsX-2.0.1.jar:?]
at com.earth2me.essentials.Essentials.onCommand(Essentials.java:424) [EssentialsX-2.0.1.jar:?]
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) [craftbukkit.jar:git-Bukkit-c373061]
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:140) [craftbukkit.jar:git-Bukkit-c373061]
at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchCommand(CraftServer.java:620) [craftbukkit.jar:git-Bukkit-c373061]
at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchServerCommand(CraftServer.java:606) [craftbukkit.jar:git-Bukkit-c373061]
at net.minecraft.server.v1_8_R3.DedicatedServer.aO(DedicatedServer.java:372) [craftbukkit.jar:git-Bukkit-c373061]
at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:336) [craftbukkit.jar:git-Bukkit-c373061]
at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:629) [craftbukkit.jar:git-Bukkit-c373061]
at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:537) [craftbukkit.jar:git-Bukkit-c373061]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_181]
[21:04:31 WARN]: java.lang.NullPointerException
[21:04:31 WARN]: at net.milkbowl.vault.chat.plugins.Chat_GroupManager.getPlayerPrefix(Chat_GroupManager.java:275)
[21:04:31 WARN]: at net.milkbowl.vault.chat.Chat.getPlayerPrefix(Chat.java:67)
[21:04:31 WARN]: at net.milkbowl.vault.chat.Chat.getPlayerPrefix(Chat.java:91)
[21:04:31 WARN]: at com.earth2me.essentials.perm.impl.AbstractVaultHandler.getPrefix(AbstractVaultHandler.java:48)
[21:04:31 WARN]: at com.earth2me.essentials.perm.PermissionsHandler.getPrefix(PermissionsHandler.java:68)
[21:04:31 WARN]: at com.earth2me.essentials.User.getNick(User.java:310)
[21:04:31 WARN]: at com.earth2me.essentials.User.getNick(User.java:279)
[21:04:31 WARN]: at com.earth2me.essentials.User.setDisplayNick(User.java:339)
[21:04:31 WARN]: at com.earth2me.essentials.commands.Commandnick.setNickname(Commandnick.java:114)
[21:04:31 WARN]: at com.earth2me.essentials.commands.Commandnick.updatePlayer(Commandnick.java:71)
[21:04:31 WARN]: at com.earth2me.essentials.commands.EssentialsLoopCommand.loopOfflinePlayers(EssentialsLoopCommand.java:54)
[21:04:31 WARN]: at com.earth2me.essentials.commands.Commandnick.run(Commandnick.java:51)
[21:04:31 WARN]: at com.earth2me.essentials.commands.EssentialsCommand.run(EssentialsCommand.java:167)
[21:04:31 WARN]: at com.earth2me.essentials.Essentials.onCommandEssentials(Essentials.java:512)
[21:04:31 WARN]: at com.earth2me.essentials.Essentials.onCommand(Essentials.java:424)
[21:04:31 WARN]: at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44)
[21:04:31 WARN]: at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:140)
[21:04:31 WARN]: at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchCommand(CraftServer.java:620)
[21:04:31 WARN]: at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchServerCommand(CraftServer.java:606)
[21:04:31 WARN]: at net.minecraft.server.v1_8_R3.DedicatedServer.aO(DedicatedServer.java:372)
[21:04:31 WARN]: at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:336)
[21:04:31 WARN]: at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:629)
[21:04:31 WARN]: at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:537)
[21:04:31 WARN]: at java.lang.Thread.run(Unknown Source)

Essentials config:
https://pastebin.com/s31USJCR

 

https://pastebin.com/He7NjNSs

 

What should I do to fix it? Reinstall Grp Manager?

 

I have 3 worlds
world
MainWorld
and
JavaLand.
My Default one is JavaLand. Im going to post that..

 

I just checked JavaLand's Users.yml. Only 3 players are registered, and they have never joined before..

the users.yml for MainWorld has NOTHING but one line of NULL.

All the users are registered on world. Gimme a second.

https://pastebin.com/bxtWMv8t

EDIT by Moderator: merged posts, please use the edit button instead of double posting.

 

Done..

/nick works now. Thanks! :3
May I know whats the cause of it in detail?

EDIT by Moderator: merged posts, please use the edit button instead of double posting.

 

Thanks!