Empty commit with i18n + nested collections (when missing a language file)

[martinjagodic]

In a nested collection that uses i18n, an entry is not saved if it's missing a language.

Consider the below structure for example. Note that posts is missing _index.sl.md.

content
│-  _index.en.md
│-  _index.sl.md
│
└──posts
│   │-  _index.en.md

Corresponding config

i18n:
  structure: multiple_files
  locales: [sl, en]

collections:
  - name: content
    label: Content
    label_singular: post
    folder: content
    i18n: true
    nested:
      depth: 10
      summary: "{{title}}"
    fields: 
      - {name: title, widget: string, i18n: true}

If you try to save the posts/_index file via CMS, it will produce an empty commit. If you add posts/_index.sl.md, the commit will save changes as expected.

I stumbled upon this bug years ago and posted it on Netlify Forums, but the post is now deleted. Thanks to the Internet Archive, we have a snapshot version: https://web.archive.org/web/20221207001621/https://answers.netlify.com/t/changes-to-entries-saved-in-the-ui-but-commit-is-empty/34954

[demshy]

just in case, we could check if proposed changes in #7145 solve this