When I go to trade with any villager, I see that there are some trades that will have an input but you can't see what the output is. I also see that some other trades will have an output present but no input. 

Example: 

On one of the trades with an input and no output, there would be one that the input is an emerald and i put in an emerald, the game then crashes because you don't know what the output is.