Ensure a not found exception is thrown when a member is not found

[proggeler]

When a request is sent to member with a member_id (email or identifier) in the url that is not present, the service would return a 400, bad request.
This should be handled as a 404, not found response and throw a NotFoundException.

An incorrect email or member_id should still return a bad request. (message: Invalid member_id)
A correct email address that is not found should throw a NotFoundException (message should be: Unknown member, Invalid member_id given)
A correct member_id should throw a NotFoundException (message: Unknown member)