Dear Maintainer,
when exporting an addressbook via the Roundcube web UI ("Export all"),
any group without members is silently ignored.
What I would expect is either that empty groups are exported, or a
warning message indicating that the respective groups without members
could not be exported and why.
In particular, I would expect that the result of "Export all" (if no
error is indicated) can be used with "Import" to recreate the original
addressbook.
Given that Roundcube exports to the vCard 3.0 format (c.f. RFC 2426),
and represents groups as values of `CATEGORIES` for each group member,
it seems impossible to actually export a group without members.
Hence, I suggest a warning message specifying that certain to be named
groups could not be exported because not having any members if that is
the case.
- Einhard Leichtfuß