ExtData3G not reporting `/dev/null` items

[bena-nasa]

Making issue so I don't forget. Right now ExtData3G does not report any items it is satisfying via a /dev/null setting. This is surprisingly harder than it should be. It needs to report only the items that get connected. Because we treat /dev/null entries as expressions this is hard. I tried, failed, and gave up on the first attempt. So making an issue to not forget as we do want it to give the same report as ExtData2G.