Don't send blank values from metadata to Rummager
Don't send blank values from metadata to Rummager

- We don't send blank (nil) values to the Publishing API so we
  shouldn't send them to Rummager either, to be consistent.

alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher,alphagov/specialist-publisher,alphagov/specialist-publisher,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher-rebuild