Specific Error

2012-08-23 20:32:35 [SEVERE] java.lang.NullPointerException
2012-08-23 20:32:35 [SEVERE]    at me.daddychurchill.CityWorld.CityWorld.getDefaultWorldGenerator(CityWorld.java:24)
2012-08-23 20:32:35 [SEVERE]    at org.bukkit.craftbukkit.CraftServer.getGenerator(CraftServer.java:957)
2012-08-23 20:32:35 [SEVERE]    at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:163)
2012-08-23 20:32:35 [SEVERE]    at net.minecraft.server.DedicatedServer.init(DedicatedServer.java:140)
2012-08-23 20:32:35 [SEVERE]    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:378)
2012-08-23 20:32:35 [SEVERE]    at net.minecraft.server.ThreadServerApplication.run(SourceFile:539)
2012-08-23 20:32:35 [SEVERE] Encountered an unexpected exception NullPointerException
java.lang.NullPointerException
        at me.daddychurchill.CityWorld.CityWorld.getDefaultWorldGenerator(CityWorld.java:24)
        at org.bukkit.craftbukkit.CraftServer.getGenerator(CraftServer.java:957)
        at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:163)
        at net.minecraft.server.DedicatedServer.init(DedicatedServer.java:140)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:378)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:539)