allow for choices to be empty in config file but not on command line

[mathisloevenich]

A config file like:

values = []

resolves in:
values=['']

it's unpleasent to have this empyt string. Instead it should be possible to just get an empty list.

[mathisloevenich]

If you work with choices, it will mess up the code.
A workaround for this is to add an empty string to choices

choices.append([''])

[mathisloevenich]

If there is no particular reason for this behaviour it would be nice to fix this,
even if it's not necessarily a bug.

[mathisloevenich]

With the new version 1.5.3 this is no longer working.
It worked on 1.2.3

[mathisloevenich]

We can simply fix this with nargs="*", but obviously this would allow to have flags with no effects

[carlfischerjba]

This is an issue with environment variables too.

VALUES= python mytest.py will set the corresponding arg to [''], overriding the default value. This is generally not what we want.

If the env var VALUES is undefined it works as expected and the default value is used for that arg.