/Riot Erros (Custom Plugin)

[06:23:39] [Server thread/INFO]: mattonfire issued server command: /riot
[06:23:39] [Server thread/ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'riot' in plugin Heist v0.1
	at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:180) ~[craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at org.bukkit.craftbukkit.v1_7_R3.CraftServer.dispatchCommand(CraftServer.java:703) ~[craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at net.minecraft.server.v1_7_R3.PlayerConnection.handleCommand(PlayerConnection.java:953) [craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at net.minecraft.server.v1_7_R3.PlayerConnection.a(PlayerConnection.java:815) [craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at net.minecraft.server.v1_7_R3.PacketPlayInChat.a(PacketPlayInChat.java:28) [craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at net.minecraft.server.v1_7_R3.PacketPlayInChat.handle(PacketPlayInChat.java:47) [craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at net.minecraft.server.v1_7_R3.NetworkManager.a(NetworkManager.java:157) [craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at net.minecraft.server.v1_7_R3.ServerConnection.c(SourceFile:134) [craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at net.minecraft.server.v1_7_R3.MinecraftServer.v(MinecraftServer.java:667) [craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at net.minecraft.server.v1_7_R3.DedicatedServer.v(DedicatedServer.java:260) [craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at net.minecraft.server.v1_7_R3.MinecraftServer.u(MinecraftServer.java:558) [craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at net.minecraft.server.v1_7_R3.MinecraftServer.run(MinecraftServer.java:469) [craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	at net.minecraft.server.v1_7_R3.ThreadServerApplication.run(SourceFile:628) [craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
Caused by: java.lang.NullPointerException
	at code.prison.main.Main.onCommand(Main.java:153) ~[?:?]
	at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[craftbukkit-dev1.7.9.jar:git-Bukkit-1.7.2-R0.3-30-ge027d69-b3058jnks]
	... 13 more