Fix expandable diffs

## What does this MR do?

Fix expandable diffs and the master build.

## Are there points in the code the reviewer needs to double check?

Nope.

## Why was this MR needed?

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4776#note_13003494

Doesn't need a CHANGELOG entry etc.

See merge request !5200