The check for <amp-experiment> in the ServerSideRendering transformer is missing a check to make sure the <amp-experiment> is not just empty.

In the Go implementation, you can see an additional isAmpExperimentUsed() check: https://github.com/ampproject/amppackager/blob/v2/transformer/transformers/serversiderendering.go#L127

I'm currently facing the issues that the spec files seem to be wrong as this check is missing, so my tests are failing here:
https://travis-ci.org/ampproject/amp-wp/jobs/640983826#L1270-L1340