[yang-doctors] when statement of an optional leaf? Does it make an optional leaf?

[Benoit Claise <[e-mail]>]

YANG doctors,

$ pyang -f tree  ietf-service-assurance.yang
module: ietf-service-assurance
   +--ro assurance-graph-version?       yang:counter32
   +--ro assurance-graph-last-change?   yang:date-and-time
   +--rw subservices
      +--rw subservice* [type id]
         +--rw type                                identityref
         +--rw id                                  string
         +--ro last-change?                        yang:date-and-time
         +--ro label?                              string
         +--rw under-maintenance?                  boolean
         +--rw maintenance-contact string <===============================
         +--rw (parameter)?
         |  +--:(service-instance-parameter)
         |     +--rw service-instance-parameter
         |        +--rw service?         string
         |        +--rw instance-name?   string
         +--ro health-score?                       uint8
         +--rw symptoms
         |  +--ro symptom* [start-date-time id]
         |     +--ro id                     string
         |     +--ro health-score-weight?   uint8
         |     +--ro label?                 string
         |     +--ro start-date-time        yang:date-and-time
         |     +--ro stop-date-time?        yang:date-and-time
         +--rw dependencies
            +--rw dependency* [type id]
               +--rw type               -> /subservices/subservice/type
               +--rw id                 -> 
/subservices/subservice[type=current()/../type]/id
               +--rw dependency-type?   identityref

The YANG modules comes from 
https://datatracker.ietf.org/doc/draft-claise-opsawg-service-assurance-yang/
Have a look at 
https://raw.githubusercontent.com/YangModels/yang/ecb622b214e59c5f6312e915d4d65823a6485852/experimental/ietf-extracted-YANG-modules/[e-mail]

The leafs in question:

           leaf under-maintenance {
             type boolean;
             default false;
             description
               "An optional flag indicating whether this particular subservice is under
               maintenance. Under this circumstance, the subservice symptoms and the
               symptoms of its dependencies in the assurance graph should not be taken
               into account. Instead, the subservice should send a 'Under Maintenance'
               single symptom.

               The operator changing the under-maintenance value must set the
               maintenance-contact variable.

               When the subservice is not under maintenance any longer, the
               under-maintenance flag must return to its default value and
               the under-maintenance-owner variable deleted.";
           }
           leaf maintenance-contact {
    when "../under-maintenance";
             type string;
             mandatory true;
             description
               "A string used to model an administratively assigned name of the
               resource that changed the under-maintenance value to 'true.

               It is suggested that this name contain one or more of the following:
               IP address, management station name, network manager's name, location,
               or phone number. In some cases the agent itself will be the owner of
               an entry. In these cases, this string shall be set to a string
               starting with 'monitor'.";
           }

In case of a leaf (maintenance-contact) with a when statement pointing 
to an optional leaf (under-maintenance), should the leaf 
(maintenance-contact) be marked as optional in the tree output?

Regards, Benoit