NULL GStrv is not always converted to empty JS array
Following up from https://bugzilla.gnome.org/show_bug.cgi?id=775679
Commit c86f34c8 doesn't seem to work for a GObject property with g_param_spec_boxed()
with type G_TYPE_STRV
. Maybe it is because we need to add a similar special case for the GI_INFO_TYPE_BOXED
case.