project = gl.projects.create({...})

project.default_branch
# None

project.files.create(
    {
        "file_path": "README",
        "branch": "master",
        "content": "Initial content",
        "commit_message": "Initial commit",
    }
)

project.default_branch
# None (not true on the server anymore)

project.refresh()

project.default_branch
# "master"