Comment 7 for bug 1355901

learned on irc one needs to have declare the attributes like this:
"attributes": {"field": "attributes", "max-count": 4},

And then have a tuple with an empty "Value" key to act I guess like a newline, like this, which works:
        us::VariantBuilder attrs;
        attrs.add_tuple({
            {"value", us::Variant(date_s.toStdString())}
        });
        attrs.add_tuple({
            {"value", us::Variant("")}
        });
        attrs.add_tuple({
            {"value", us::Variant(time_s.toStdString())}
        });
        attrs.add_tuple({
            {"value", us::Variant("")}
        });
        res["attributes"] = attrs.end()