https://gerrit.wikimedia.org/r/c/mediawiki/extensions/GrowthExperiments/+/654580 removed a qqq message, which was the empty string (while at the same time adding translations for that message, so it doesn't seem like a merge conflict type of thing). That broke CI for subsequent patches.
Outcome
Definitions, translation and message documentation with no content are treated in the same way as those with content to avoid build/CI failures that require those presence. Such messages are highlighted on import to translation admins.