_primary_email was an array to be able to use it directly in the
depends. Typically a 'depends' with a computed value (lambda) needs
an array. Otherwise, it will only take the first character of the
field name string.
By setting _primary_email as a string, the lambda should always get
an array. But it simplifies a lot the usage of the _primary_email.
also, having an array was confusing as we could think that more than
one field can be considered as the primary email. This is not the
goal hare. So having the _primary_email as a single string is more
'self describing'. Only one field should be the _primary_email.
David Beguin
692f0062fb