1. Fields that are mandatory, but we do not support them:

• nat/instances/instance/connection-limits/limit-per-instance
  Action: ask draft editors to remove it if possible
• nat/instances/instance/policy/port-set/port-set-size
  this one might be ODL missing feature, because port-set is defined using when statement:

container port-set {
    when "../port-allocation-type = 'port-range-allocation'";
    [...]
}

Action: open jira ticket for ODL yangtools and get it confirmed