Set Assertion ENV var when attribute is empty

[Peter Schober]

* Tom Noonan <tom at joinroot.com> [2019-03-14 17:38]:
> I'm setting up some custom attribute through SPv3 and running into some
> headaches with empty values.  Our IdP defaults to empty if an attribute
> hasn't been set on a user's profile:

AFAIR that's not legal in SAML (empty strings, empty attributes),
but either way maybe the IDP should do things differently.
-peter