Client should ensure, that the payload should be empty, when not filled.

[withanage]

https://github.com/pkp/pkp-lib/discussions/10190#discussioncomment-10451009

{"invitationData":{"email":"coauthor@mailinator.com","orcid":"","givenName":{"en":"","fr_CA":""},"userGroupsToAdd":[{"userGroupId":null,"dateStart":null,"dateEnd":null,"masthead":null}]}}

Above code would not be validated. Therefore, the givenName should be removed , if not filled.