We are thinking about creating an identity schema, that has email and username as two possible identifiers. Email is mandatory and username optional in our case. When we submit a registration form with an email and a username and one of them already exists, I get an error 4000007 back (“An account with the same identifier (email, phone, username, ...) exists already.“). But it’s the same error for both cases. Is there a way to distinguish what already exists, the email address or the username? And if that does not exist, will you add it?