Fix unexpected error when installing editable packages

[frostming]

The issue

When Pipfile doesn't exist, project.pipfile_location is None, causing error when building exceptions message.

• Pipenv install does not provide a good error message for no Pipfile. #2846
• Closes Installing editable dependency in empty dir gives unhelpful message #3206

The fix

1. Don't prevent installing editable packages in empty dir.
2. Don't pass None values, use the default instead.

The checklist

• Associated issue
• A news fragment in the news/ directory to describe this fix with the extension .bugfix, .feature, .behavior, .doc. .vendor. or .trivial (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.

[frostming]

I am sure the condition skip_lock or deploy isn't what we want. Just can't find the appropriate one for now. Any suggestions?

[techalchemy]

I am not sure if I have a competing fix for this, I have a cascade of changes going on due to a release-blocking (but necessary) refactor of some code in requirementslib which is why I'm slow at the moment.

I know you're on the other side of the world, but if you're on any sychnronous platforms like slack/IRC/something else you can find me on one of those also. Would love to ask you something if possible also

[frostming]

That would be very nice. I am very glad to be invited.

[techalchemy]

I am on IRC most of the time in #pypa and #pypa-dev on https://freenode.net/ -- we have a channel over on https://pyslackers.com/ as well and i'm responsive to messages there; I have a discourse forum set up but that's not being used much -- we haven't gone beyond this yet but we're kind of waiting for someone to decide on something they prefer

[frostming]

Close in favor of #3209