[PATCH] cli: allow empty strings for notmuch insert --folder argument

[David Bremner]

Jani Nikula <jani at nikula.org> writes:

> Now that it's easy to add argument specific modifiers in opt
> descriptions, add a new .allow_empty field to allow empty strings for
> individual string arguments while retaining strict checks
> elsewhere. Use this for notmuch insert --folder, where the empty
> string means top level folder.
>

Series pushed to master.

d