java.lang.NullPointerException: Unexpected error
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at thecodex6824.thaumicaugmentation.common.block.BlockTASlab$Half$1.func_77667_c(BlockTASlab.java:78)
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at net.silentchaos512.wit.info.ObjectInfo.(ObjectInfo.java:78)
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at net.silentchaos512.wit.info.ItemStackInfo.(ItemStackInfo.java:31)
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at net.silentchaos512.wit.info.BlockStackInfo.(BlockStackInfo.java:43)
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at net.silentchaos512.wit.WIT.getRenderObject(WIT.java:207)
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at net.silentchaos512.wit.WIT.onRenderOverlay(WIT.java:245)
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at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_1089_WIT_onRenderOverlay_RenderGameOverlayEvent.invoke(.dynamic)
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at net.minecraftforge.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:90)
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at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:182)
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at net.minecraftforge.client.GuiIngameForge.post(GuiIngameForge.java:911)
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at net.minecraftforge.client.GuiIngameForge.renderHUDText(GuiIngameForge.java:741)
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at net.minecraftforge.client.GuiIngameForge.func_175180_a(GuiIngameForge.java:173)
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at net.minecraft.client.renderer.EntityRenderer.func_181560_a(EntityRenderer.java:1098)
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at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:1119)
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at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:398)
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at net.minecraft.client.main.Main.main(SourceFile:123)
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at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
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at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
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at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
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at java.lang.reflect.Method.invoke(Method.java:497)
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at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
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at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

Your "WIT" mod seems to assume that all blockstate metadata combinations are applicable to items, which is false. I'll add a check in to prevent the game from crashing if this happens, but the variant of slab that mod thinks it is will probably be wrong.

ah, that's good. The "WIT" mod is "What Is That", I think