[scim] Filtering against Null Attribute Values

[Shelley <[e-mail]>]

Do the SCIM specifications prescribe any special behavior for filtering and
sorting by attributes that are null/unspecified?

For instance, given an optional user extension attribute for "age" and the
following filters:

   - filter=age lt 18
   - filter=age gt 18

Would either of these filters return a user resource with no specified age,
such that nulls have a prescribed ordering? Or, would both of these filters
exclude all users without specified ages? (And, if it's the latter, what
effect is negation intended to have on the filter?)

This question applies to filters, matching resources during PATCH, sorting,
and other attribute operators as well (e.g. would not (displayName co
"test") match users without display names?).

Thanks in advance for any clarifications!