mod_storage_xep0227: be defensive against empty vCard An empty vCard store may look like the empty table, which does not have the `attr` key, which would then blow up in util.stanza.deserialize.

return {
  _all = {
  },
  default = {
    ["exclude-tags"] = "mod_bosh,storage,SLOW";
  };
  bosh = {
    tags = "mod_bosh";
  };
  storage = {
    tags = "storage";
  };
}