line called that NPE's volcanoGen.generate(worldObj, i, j, abyte0);

java.lang.NullPointerException
	at net.minecraft.src.ChunkProviderTropics.provideChunk(ChunkProviderTropics.java:283)
	at net.minecraft.src.ChunkProvider.loadChunk(ChunkProvider.java:67)
	at net.minecraft.src.ChunkProvider.provideChunk(ChunkProvider.java:85)
	at net.minecraft.src.World.getChunkFromChunkCoords(World.java:474)
	at net.minecraft.src.World.getBlockId(World.java:405)
	at net.minecraft.client.Minecraft.preloadWorld(Minecraft.java:1833)
	at net.minecraft.client.Minecraft.changeWorld(Minecraft.java:1744)
	at net.minecraft.src.DimensionBase.changeWorld(DimensionBase.java:145)
	at net.minecraft.src.DimensionBase.usePortal(DimensionBase.java:84)
	at net.minecraft.src.ItemTropicsPortalStarter.onItemRightClick(ItemTropicsPortalStarter.java:28)
	at net.minecraft.src.ItemStack.useItemRightClick(ItemStack.java:101)
	at net.minecraft.src.PlayerController.sendUseItem(PlayerController.java:54)
	at net.minecraft.client.Minecraft.clickMouse(Minecraft.java:1179)
	at net.minecraft.client.Minecraft.runTick(Minecraft.java:1499)
	at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:694)
	at net.minecraft.client.Minecraft.run(Minecraft.java:634)
	at java.lang.Thread.run(Unknown Source)