Unable to remove cover type and version

I'm trying to remove the 'cover type' and 'cover version' (set them to blank/nothing.) If I put the following in project.properties:

maven.pdf.cover.type=
maven.pdf.cover.version=

I get the text '-PARAM' for the cover type, and 'v1.0' for the cover version.

If I try it again with '.' for both of those properties, cover type works (just prints a dot) but cover version prints 'v..'.

This seems to call for something like a 'maven.pdf.cover.version.prefix' property (that can be set to blank.)