Missign app/assets folder since 10.8.0


Since using https://hub.docker.com/r/gitlab/gitlab-ce/ at 10.8.0 (10.7.3 before), the app/assets folder seems to be missing.
It’s a big problem for me since I do theme modifications in this folder before recompiling assets.
I searched a lot in the code but couldn’t find the cause of this. Could anyone tell me if this is expected, and if so, what is causing this?