this is a bit iffy .. this method does not exist in the ``FormatNegotiatorInterface``.

so we either:
1) set the media type in the ``FormatNegotiator`` and leave this class unchanged, which is sort of a surprising side effect from calling ``getBestFormat()``
2) add a new interface that if used in the injected format negotiator triggers the new logic, which is a bit annoying since we would have to maintain duplicate logic