In chat : An internal error occured while attempting to perform this command

In console :

[01:54:28] [Server thread/INFO]: SkyHeroesDada11 issued server command: /f warp
[01:54:28] [Server thread/ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'f' in plugin Factions v1.6.9.5-U0.2.1-RC-1.6.2-RC-2.4-BETA
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) ~[spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at org.bukkit.craftbukkit.v1_12_R1.CraftServer.dispatchCommand(CraftServer.java:648) ~[spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at net.minecraft.server.v1_12_R1.PlayerConnection.handleCommand(PlayerConnection.java:1397) [spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at net.minecraft.server.v1_12_R1.PlayerConnection.a(PlayerConnection.java:1232) [spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at net.minecraft.server.v1_12_R1.PacketPlayInChat.a(PacketPlayInChat.java:45) [spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at net.minecraft.server.v1_12_R1.PacketPlayInChat.a(PacketPlayInChat.java:1) [spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at net.minecraft.server.v1_12_R1.PlayerConnectionUtils$1.run(SourceFile:13) [spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_202]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_202]
    at net.minecraft.server.v1_12_R1.SystemUtils.a(SourceFile:46) [spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:748) [spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:406) [spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:679) [spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:577) [spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    at java.lang.Thread.run(Thread.java:748) [?:1.8.0_202]
Caused by: java.lang.NullPointerException
    at com.massivecraft.factions.util.WarpGUI.buildDummyItem(WarpGUI.java:226) ~[?:?]
    at com.massivecraft.factions.util.WarpGUI.buildDummyItems(WarpGUI.java:200) ~[?:?]
    at com.massivecraft.factions.util.WarpGUI.build(WarpGUI.java:64) ~[?:?]
    at com.massivecraft.factions.cmd.CmdFWarp.perform(CmdFWarp.java:46) ~[?:?]
    at com.massivecraft.factions.zcore.MCommand.execute(MCommand.java:126) ~[?:?]
    at com.massivecraft.factions.cmd.FCommand.execute(FCommand.java:62) ~[?:?]
    at com.massivecraft.factions.zcore.MCommand.execute(MCommand.java:112) ~[?:?]
    at com.massivecraft.factions.cmd.FCommand.execute(FCommand.java:62) ~[?:?]
    at com.massivecraft.factions.zcore.MCommand.execute(MCommand.java:130) ~[?:?]
    at com.massivecraft.factions.zcore.MPlugin.handleCommand(MPlugin.java:288) ~[?:?]
    at com.massivecraft.factions.zcore.MPlugin.handleCommand(MPlugin.java:251) ~[?:?]
    at com.massivecraft.factions.SavageFactions.handleCommand(SavageFactions.java:436) ~[?:?]
    at com.massivecraft.factions.SavageFactions.onCommand(SavageFactions.java:447) ~[?:?]
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[spigot-1.12.2.jar:git-Spigot-4bd94dc-fb414fe]
    ... 15 more