Fix for env var precedence and to for File provider required field

[autodidaddict]

• Fix so the lack of an environment variable subsequent in a pipeline won't cause it to wipe previously established values
• Fix so that the File provider now honors the required field (previously ignored, non-required but missing files would cause a crash)

[autodidaddict]

@keathley just checking in to see if this is something that might get looked at?

[bsedat]

As a note for anyone else, an equivalent patch can also be made to the File provider to allow it to supersede env var bindings when an overridden attribute is missing from the file.

[brooksmtownsend]

Hey @keathley / @bgmarx , is this something that's being considered?

[mhanberg]

@autodidaddict do you mind adding a unit test for these two cases? And also maybe an example scenario in the PR description? I think I understand the precedence problem you're describing but it would be great to have an actual example to see.

Thanks!

[autodidaddict]

just checking in since it's been a while and I didn't remember your comment from June. we've been using this fork in production for right around a year now. Do you still want the unit tests, etc @mhanberg ?