Don't store _old_ if we're passed nil

[artfuldodger]

Saying, for example user.update(avatar: nil) will result with the avatar_filename set to "old", which is unexpected.

[rmm5t]

Sorry for the awful delay here. Thanks to #179, and after a hiatus, I'm now in the process of catching up with things on this project.

If this issue is still a problem, could you please rebase on master to get the test suite green for this PR?

[artfuldodger]

@rmm5t No worries! I rebased off master, but I'm not sure if this change is still necessary. Will try to play around some more to see.

[simonc]

Hello there. We're facing this exact issue so I think this change is still necessary 🙂

[simonc]

That being said, testing this PR in a custom fork it seems that it should be new_file.path.nil? instead.

[rmm5t]

@artfuldodger @simonc Sorry for the long delay with this PR. Would someone be willing to investigate this further while also adding a spec to confirm behavior?

[artfuldodger]

I'm not using Mongo any more, so I'm of no use here