Allow empty string for release in apt::source

[tomduckering]

This fixes a regression from commit 0a178c3.

Some repos don't have a release. This allows using such repos.

Tests added to make sure when release is set to an empty string the
source file is rendered correctly.

All other tests are passing.

[tomduckering]

This is the original fix: #78

[tomduckering]

Related forge issue: https://tickets.puppetlabs.com/browse/FORGE-361

[NeatNerdPrime]

Really interested that this PR gets accepted. It's a blocking feature for us a.t.m. And for now we have to modify it on our own puppet master, but preferably this should be in the current master branch

[NeatNerdPrime]

@HelenCampbell Sorry to ping you directly, but i'd really like to bring this PR into puppetlabs'es attention. It will be really useful. some conflicts need to be resolved though.

[HelenCampbell]

Hey @NeatNerdPrime , no problems on the ping!
I've been playing about with this today and since the module has moved on quite a bit since this PR I took the test addition from here and ran it on the latest master and it's passed. So to a degree I'm confident that this issue is fixed within the latest version of apt and upgrading to use 4.0.0 may fix your issue!
The new functionality can be seen here:
https://github.com/puppetlabs/puppetlabs-apt/blob/master/manifests/source.pp#L23
I'll do further research into this and most probably will add the test regardless.

[NeatNerdPrime]

@HelenCampbell Thank you for your comment! Currently we are using puppetlabs-apt v 4.0.0 taken from the forge, not the github version. I'm wondering if there is a difference between the codebase from forge version 4.0.0 and github's master version. Both their metadata.json file indictate they are the same version.

Guess @tomduckering and myself will patiently await your R&T results. Enjoy your day!

[HelenCampbell]

@tomduckering @NeatNerdPrime Rebased this work:
#681
Still need to make adjustments but will do that on Tuesday when I'm back in the office and will follow up with a new release of apt to ensure the forge version is where it should be!

[HelenCampbell]

@tomduckering @NeatNerdPrime #681 Has been merged so closing this PR - apt is now pending release so should go out in the next week or two. Thanks guys!