Crash report only points to Crafting GUI.

Stacktrace:
at net.minecraft.item.ItemStack.func_77980_a(ItemStack.java:415)
at net.minecraft.inventory.SlotCrafting.func_75208_c(SlotCrafting.java:52)
at net.minecraft.inventory.SlotCrafting.func_75210_a(SlotCrafting.java:45)
at net.minecraft.inventory.Slot.func_75220_a(Slot.java:34)
at net.minecraft.inventory.ContainerWorkbench.func_82846_b(SourceFile:96)
at net.minecraft.inventory.Container.func_75144_a(Container.java:246)
at net.minecraft.client.multiplayer.PlayerControllerMP.func_78753_a(PlayerControllerMP.java:488)
at net.minecraft.client.gui.inventory.GuiContainer.func_146984_a(GuiContainer.java:629)
at net.minecraft.client.gui.inventory.GuiContainer.func_73864_a(GuiContainer.java:388)
at net.minecraft.client.gui.GuiScreen.func_146274_d(GuiScreen.java:554)
at net.minecraft.client.gui.GuiScreen.func_146269_k(GuiScreen.java:523)

— Affected screen —
Details:
Screen name: net.minecraft.client.gui.inventory.GuiCrafting