Are Objects' and Object References' `uuid` field mandatory?

[0xThiebaut]

The MISP Core RFC does not specify whether for an Object and an Object Reference the uuid attribute MUST, SHALL or MAY be present. The following is the extract of the description of an Object's uuid attribute:

uuid represents the Universally Unique IDentifier (UUID) [RFC4122] of the object reference. The uuid MUST be preserved for any updates or transfer of the same object reference. UUID version 4 is RECOMMENDED when assigning it to a new object reference.

As an example, the uuid attribute of an Attribute has its presence described as follow:

uuid represents the Universally Unique IDentifier (UUID) [RFC4122] of the event. The uuid MUST be preserved for any updates or transfer of the same event. UUID version 4 is RECOMMENDED when assigning it to a new event.

uuid is represented as a JSON string. uuid MUST be present.

The description of both an Object and Object Reference do not provide further information on the uuid attribute.