[18:38:43 ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'gm' in plugin Server v1.0
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:140) ~[craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at org.bukkit.craftbukkit.v1_12_R1.CraftServer.dispatchCommand(CraftServer.java:621) ~[craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at net.minecraft.server.v1_12_R1.PlayerConnection.handleCommand(PlayerConnection.java:1326) [craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at net.minecraft.server.v1_12_R1.PlayerConnection.a(PlayerConnection.java:1186) [craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at net.minecraft.server.v1_12_R1.PacketPlayInChat.a(SourceFile:37) [craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at net.minecraft.server.v1_12_R1.PacketPlayInChat.a(SourceFile:9) [craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at net.minecraft.server.v1_12_R1.PlayerConnectionUtils$1.run(SourceFile:13) [craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_172]
        at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_172]
        at net.minecraft.server.v1_12_R1.SystemUtils.a(SourceFile:46) [craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:695) [craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:370) [craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:650) [craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:554) [craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        at java.lang.Thread.run(Thread.java:748) [?:1.8.0_172]
Caused by: java.lang.ArrayIndexOutOfBoundsException: 0
        at server.main.CommandSetGamemode.onCommand(CommandSetGamemode.java:19) ~[?:?]
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[craftbukkit-1.12.jar:git-Bukkit-9a1fc1e]
        ... 15 more