12:32:10 [WARNING] Task of 'Mobs' generated an exception
java.lang.NullPointerException
        at me.coldandtired.mobs.Area.<init>(Area.java:22)
        at me.coldandtired.mobs.Mob_spawner.spawn_mobs(Mob_spawner.java:37)
        at me.coldandtired.mobs.Mob_spawner.run(Mob_spawner.java:52)
        at org.bukkit.craftbukkit.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:137)
        at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:493)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:425)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:457)
12:32:27 [SEVERE] java.lang.NullPointerException
12:32:27 [SEVERE]       at net.minecraft.server.Packet.b(Packet.java:151)
12:32:27 [SEVERE]       at net.minecraft.server.Packet107SetCreativeSlot.a(SourceFile:25)
12:32:27 [SEVERE]       at net.minecraft.server.Packet.a(Packet.java:79)
12:32:27 [SEVERE]       at net.minecraft.server.NetworkManager.h(NetworkManager.java:149)
12:32:27 [SEVERE]       at net.minecraft.server.NetworkManager.c(NetworkManager.java:263)
12:32:27 [SEVERE]       at net.minecraft.server.NetworkReaderThread.run(SourceFile:77)