Comment 12 for bug 1778591

This bug is still relevant. Excerpt from https://review.openstack.org/#/c/579163/:

The current behavior

  status: 200
  {
      "allocations": {}
  }

is wrong because the response payload doesn't conform to the expected format, which would contain a consumer_generation, project_id, and user_id. That those fields don't make sense in a context where there's no consumer is another motivator for making this a 4xx failure.