In case the identifier attribtue was missing we were defaulting to an empty string,
which (1) isn't really correct and (2) is not a valid identifier for api-platform
and makes it fail when serializig API responses.

Avoid this by ignoring all LDAP users without an identifier.

Some setters got stricter and no longer allow setting null, so
fix the tests.

So the user can decide between SSL/TLS.
We still default to encryption on and use the default ports since
no one required something different until now and
to not bloat the config.