Currently blocking the backport of: https://gerrit.wikimedia.org/r/#/q/801c39d3fe6500fb0eb4a5767d5987f9ba78107c
Which is, in turn, blocking other backports which is, in turn, blocking the wmf.5 train.
From IRC:
<legoktm> Wikibase's phan config only loads the Babel/PageImages phan stubs if extensions/Babel (etc.) is not a directory <legoktm> but on wmf/ branches that is always a directory since it's a submodule <legoktm> maybe it should check for some thing like file_exists(extensions/Babel/extension.json)