recent versions don't set empty tag values any more

[david-its]

It is important to set empty tag values sometimes:

• e.g. for download links to open one has to set download=""
• for Tab pages to be openable by right click in another browser Tab <a> element should have an empty href="" value. Otherwise Chrome won't even show "Open Link in New Tab/Window" menu items.

however, in recent versions there was a change in pkg/app/attribute.go:

func (a attributes) Set(name string, value any) {
...
        if v != "" {
                a[name] = v
        }
}

which broke old behavior.
can we revert it back please? i don't think it's good idea to list here all the possible exceptions.