Pulp

You can create a distribution without a publication but once you set publication on a distribution, you can't unset it.

$ http POST :8000/pulp/api/v3/distributions/ name=test base_path=test
# 200
$ http PATCH :8000/pulp/api/v3/distributions/320f93b3-79e4-4425-ba99-15338284979c/ publication=/pulp/api/v3/publications/6529920f-9507-4ec0-bb09-50afa31b1685/
# 200
$ http PATCH :8000/pulp/api/v3/distributions/320f93b3-79e4-4425-ba99-15338284979c/ publication=
# 400
{
    "publication": [
        "This field may not be null."
    ]
}