IdPv3 direct NameID mapping default

[Scott Koranda]

Hello,

The default for IdPv3 for direct NameID mapping as recorded in
subject-c14n.xml in the shibboleth.NameTransformPredicate is
an empty whitelist--no relying parties by default can complete
an attribute query with a direct NameID mapping.

I am curious why that is the default?

Thanks,

Scott K