Skip post processor execution if field is empty.

[serveral1]

So I have the following post processing task for kemono that writes a html file for the embed field:
"embeded-content-id": { "name": "metadata", "event": "post", "mode": "custom", "format": "{embed[url]}", "filename": "{id}-e.html" },
However I'd like for it to only be executed when the embed field is not empty so that I don't end up with hundreds of empty html files. I tried to add a "filter": "embed is not None", option but so far I haven't had much luck in doing so.

[mikf]

"filter": "embed"

Yes, that's really it.