ZOMBIES 4 R3AL

Hello, I currently am running a server and I want to update to 1.4.6 (currently running 1.4.5) and I want to keep the world, just update the mods, but when I use the updated forge I get a NullPointerException with this: at net.minecraftforge.common.ForgeChunkManager.loadWorld(ForgeChunkManager.java:527) at net.minecraftforge.common.ForgeInternalHandler.onDimensionLoad(ForgeInternalHandler.java:71) at net.minecraftforge.event.ASMEventHandler_1_ForgeInternalHandler_onDimensionLoad_Load.invoke(.dynamic) at net.minecraftforge.event.ASMEventHandler.invoke(ASMEventHandler.java:35) at net.minecraftforge.event.EventBus.post(EventBus.java:103) at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:279) at ho.c(DedicatedServer.java:179) at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:458) at fy.run(SourceFile:849) Now I had a look at this and the new update and as of 4.6.12.511 I see they have removed the common folder, and it looks to me that it is still looking for whatever is in the common folder (I'm not a modder so I really don't know what it means, just me guessing). So I thought is there a way to convert your world to this new forge build without the common folder without having to create a new world? Thanks.