Currently, in order to make use of the Charactermancer in custom sheet development you need to tie it to a compendium. The work around for unsupported systems and homebrews is to add a compendium from another game to enable the functionality and then just ignore it. It would be cleaner/nicer, and hopefully minimal lift required if Roll20 could add a generic empty compendium with no entries. That would at least improve the experience for people building/using custom sheets and provide a bridge to improve the experience for homebrewers and people playing niche small press games since we still don't have custom compendiums.