Given a selectbox field bound to users (for example bound to project members), and given an artifact having a user selected as the field value, if this user is no more a project members, then this value is no more a valid one.
If we update this artifact with the Artifact UI, then this value is cleared and
None is selected.
If we update this artifact with the Artifact modal, then this value is not cleared even if
None is selected and an error is raised.