- There's been no explicit support having argument void type
as you would not be able to use with annotation model but
surely can be wrapped as Type with CommandRegistration.
- For now change CommandInfoModel so that it uses empty string
which is i.e. expected in help options which are just
used as flags.
- It's outside of this commit to change parser to fail if
user gives an argument value for this type of options.
- Fixes#586
f5d6bae117