Editable requirements (-e) raises "DistributionNotFound: The 'None' distribution was not found"

[bagerard]

Editable requirements, i.e: rows like this one
-e file:some_internal_package # via -r requirements.in

Are currently making this library fail with pkg_resources.DistributionNotFound: The 'None' distribution was not found and is required by the application

This is kind of related to #33 but although error message is the same, it is actually a different problem as that one relates to git+https:// construct, and this one, to the -e construct