[GreySloth]

The default value displayed looks blank, I have no idea what is in the DB or how to manually look at the data in the DB, or how to FIND what it uses to represent 'no value'.

I do notice that if I use no filters and no renames, it creates a bunch of collections of the form yyyy-mm-dd (this is not the date format I use for the displayed data in calibre). All of the names are valid dates (none of them could be used to represent 'no value').

I really suspect that what ever Calibre uses to represent 'no value' would result in a invalid collection name, and that the plugin is discarding these without passing them to the filters or rename logic.

I would be willing to try to look at the DB manually, but would need instructions ....

Thanks