Allow NULL schema for certain service methods
Allow NULL schema for certain service methods

 * So that we can work without a schema from the secret-tool
 * Users can handle the schema on their own if desired, using
   the 'Complete API'

stefwalter/libsecret,GNOME/libsecret,Distrotech/libsecret,stefwalter/libsecret,GNOME/libsecret,GNOME/libsecret,Distrotech/libsecret,Distrotech/libsecret,stefwalter/libsecret,GNOME/libsecret,Distrotech/libsecret,stefwalter/libsecret,stefwalter/libsecret,Distrotech/libsecret