If one enter a room as external user and doesn't provide first or surname, this empty string will handled different in the room (see screenshot). Provide just one of this might be senseful depends on the context.
If both are empty, predefined first and surnames will be generated but dialogue is asking for an E-Mail (see screenshot). Existence will not be proofed, so there is no sense to ask for it.
Style name like in the user area and just skip mail dialogue and use the default names would be enough for me