Record default filler removes populated fields

[rainest]

#302 introduced a bug that was not visible until integrated into another application.

bug.tar.gz shows a demonstration using deck. Syncing orig.yaml with the current deck release (/tmp/deck) and then diffing with a build that includes 0.39.1 shows it removing the populated config.add.headers array.

[rainest]

@nishant95 the change from #302 introduced a bug where it's stripping present configuration. Can you see if you can find a fix?

[nishant95]

@rainest Sure, i'll look into it.

[nishant95]

@rainest raised a PR #309 with the fix.

Can we add some checks so that such bugs can be detected before merging the PR?

[rainest]

We can't easily add consistent checks beyond the style of tests already in this repo since it'd mean running other repo's tests.

I should have run a manual replace test like Kong/kubernetes-ingress-controller#3866 earlier.

Ed: well, that's what I wanted to do, anyway. For some reason that doesn't appear to be triggering PR integration tests like it should :(

[nishant95]

Fixed in #309