[16:35:20 INFO]: _Elements issued server command: /slot build default
[16:35:20 ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'slot' in plugin ItemSlotMachine v1.3.1
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot.jar:git-Spigot-1541]
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:181) ~[spigot.jar:git-Spigot-1541]
        at org.bukkit.craftbukkit.v1_7_R3.CraftServer.dispatchCommand(CraftServer.java:767) ~[spigot.jar:git-Spigot-1541]
        at net.minecraft.server.v1_7_R3.PlayerConnection.handleCommand(PlayerConnection.java:1015) [spigot.jar:git-Spigot-1541]
        at net.minecraft.server.v1_7_R3.PlayerConnection.a(PlayerConnection.java:845) [spigot.jar:git-Spigot-1541]
        at net.minecraft.server.v1_7_R3.PacketPlayInChat.a(PacketPlayInChat.java:28) [spigot.jar:git-Spigot-1541]
        at net.minecraft.server.v1_7_R3.PacketPlayInChat.handle(PacketPlayInChat.java:65) [spigot.jar:git-Spigot-1541]
        at net.minecraft.server.v1_7_R3.NetworkManager.a(NetworkManager.java:184) [spigot.jar:git-Spigot-1541]
        at net.minecraft.server.v1_7_R3.ServerConnection.c(ServerConnection.java:81) [spigot.jar:git-Spigot-1541]
        at net.minecraft.server.v1_7_R3.MinecraftServer.v(MinecraftServer.java:731) [spigot.jar:git-Spigot-1541]
        at net.minecraft.server.v1_7_R3.DedicatedServer.v(DedicatedServer.java:284) [spigot.jar:git-Spigot-1541]
        at net.minecraft.server.v1_7_R3.MinecraftServer.u(MinecraftServer.java:584) [spigot.jar:git-Spigot-1541]
        at net.minecraft.server.v1_7_R3.MinecraftServer.run(MinecraftServer.java:490) [spigot.jar:git-Spigot-1541]
        at net.minecraft.server.v1_7_R3.ThreadServerApplication.run(SourceFile:628) [spigot.jar:git-Spigot-1541]
Caused by: java.lang.NullPointerException