Missing language string in admin console

[phette23]

Describe the bug
There's a com.equella.admin.validation.incomplete language string which isn't defined in any of the reference language packs (I downloaded all of them from 2019.2 up to the most recent release, 2021.1.2).

To Reproduce
Steps to reproduce the behavior:

1. Launch the admin console
2. Edit a collection
3. Go to Display then Search Results Template tab
4. Add a new field to the search results template at the bottom
5. Don't fill it out complete (e.g. leave the metadata node or data type undefined)
6. Try to Save the collection
7. See error with missing language string

There are probably other ways of triggering this "validation incomplete" message but this was the one where I discovered it.

Expected behavior

A message should appear, even if you've not explicitly defined one in your language pack. But in the absence of that, there should be some language pack that tells you what the message would usually say, yet none of the releases have this property.

Platform:

• OpenEquella Version: 2019.2
• OS: macOS 12.0.1 21A559 x86_64
• Using admin console, not a web browser, and I assume this bug is present regardless of oE version since I don't see the property in even the most recent versions' language packs