Server 500 error when you try to generate a PDF for which you have no favorite parts
When you try to generate a PDF for a repertoire for which you have not chosen any favorite parts, you get a server 500 error.
A potential solution for this is redisplaying the repertoire page, but using the message system introduced in !114 (merged) to inform the user that they haven't chosen any favorite parts yet. I think this is better than hiding the button, since it would hide the entire feature. Showing a message makes the generation more discoverable by the user.
This issue might be superseded by a larger overhaul to the system for choosing your favorite parts.