The coin bag works perfectly fine in survival but if you are in creative and you are burning iron and/or steel and have no nuggets in your inventory the bag doesn't throw a coin/nugget but I think it does try to make a blue line follow it but since there was no coin to follow Minecraft crashes with a null pointer.

So I think there needs to be a check on the right click event for the coin bag that even in creative it won't work if you have no coins on you, that would fix the crash issue.