Would it be possible to grab the lexicon title some other way? Currently you're calling

Minecraft.getMinecraft().thePlayer.getCurrentEquippedItem().getDisplayName();

Which I know in normal cases should always be fine. But in Enchiridion 2, I'm opening books without a physical item in hand. (Obviously putting one there temporarily to get the books open at least). Currently I'm pretty much having to override your guis so that they don't crash because of this line.