---
upgrade:
  - imageRef input to the REST API is now restricted
    to be UUID or an empty string only. imageRef
    input while create, rebuild and rescue server etc
    must be a valid UUID now. Previously, a random
    image ref url containing image UUID was accepted.
    But now all the reference of imageRef must be a
    valid UUID (with below exception) otherwise API
    will return 400.

    Exception- In case boot server from volume.
    Previously empty string was allowed in imageRef
    and which is ok in case of boot from volume.
    Nova will keep the same behavior and allow empty
    string in case of boot from volume only and 400
    in all other case.