notmuch-emacs: Fcc to top-level directory given by database.path

[Jani Nikula]

On Sat, 23 Sep 2017, David Bremner <david at tethera.net> wrote:
> Do you happen to know if it calls with an empty string as the folder
> name? It would be consistent with searching for that to insert at the
> top level.

notmuch insert --folder= or --folder="" does not work:

String argument for option "folder" must be non-empty.
Unrecognized option: --folder=

It seems that our argument parser doesn't accept empty strings at all,
which is a bit of a limitation. It would be logical for the empty string
to work here, and AFAICT the notmuch insert code would handle this if
the argument was let through the parsing.

BR,
Jani.