[13:15:44] [Server thread/INFO] [minecraft/NetHandlerPlayServer]: Coivated issued server command: /gamemode 1

[13:15:44] [Server thread/ERROR] [minecraft/NetHandlerPlayServer]: null

org.bukkit.command.CommandException: Unhandled exception executing 'gamemode 1' in org.bukkit.craftbukkit.v1_12_R1.command.VanillaCommandWrapper(gamemode)

        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:148) ~[SimpleCommandMap.class:?]

        at org.bukkit.craftbukkit.v1_12_R1.CraftServer.dispatchCommand(CraftServer.java:682) ~[CraftServer.class:master-70eda1f]

        at net.minecraft.network.NetHandlerPlayServer.func_147361_d(NetHandlerPlayServer.java:1449) [pa.class:?]

        at net.minecraft.network.NetHandlerPlayServer.func_147354_a(NetHandlerPlayServer.java:1307) [pa.class:?]

        at net.minecraft.network.play.client.CPacketChatMessage.func_148833_a(CPacketChatMessage.java:42) [la.class:?]

        at net.minecraft.network.play.client.CPacketChatMessage.func_148833_a(CPacketChatMessage.java:9) [la.class:?]

        at net.minecraft.network.PacketThreadUtil$1.run(PacketThreadUtil.java:10) [hv$1.class:?]

        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.8.0_261]

        at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.8.0_261]

        at net.minecraft.util.Util.func_181617_a(Util.java:36) [h.class:?]

        at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:692) [MinecraftServer.class:?]

        at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:394) [nz.class:?]

        at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:635) [MinecraftServer.class:?]

        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:528) [MinecraftServer.class:?]

        at java.lang.Thread.run(Unknown Source) [?:1.8.0_261]

Caused by: java.lang.IndexOutOfBoundsException: Index: 7, Size: 7

        at java.util.ArrayList.rangeCheck(Unknown Source) ~[?:1.8.0_261]

        at java.util.ArrayList.get(Unknown Source) ~[?:1.8.0_261]

        at org.bukkit.craftbukkit.v1_12_R1.command.VanillaCommandWrapper.dispatchVanillaCommand(VanillaCommandWrapper.java:86) ~[VanillaCommandWrapper.class:master-70eda1f]

        at org.bukkit.craftbukkit.v1_12_R1.command.VanillaCommandWrapper.execute(VanillaCommandWrapper.java:54) ~[VanillaCommandWrapper.class:master-70eda1f]

        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) ~[SimpleCommandMap.class:?]

        ... 14 more

서버를 열어서 명령어를 치니까 이렇게 뜨는데 어떻게 하죠