secret-password: Mark @schema argument nullable for *v functions
secret-password: Mark @schema argument nullable for *v functions

Given these functions take a hash table built from valid attributes,
there is no need to re-validate.  This is also consistent with the
secret_service API.

GNOME/libsecret,GNOME/libsecret,GNOME/libsecret,GNOME/libsecret