More fun with GAM, removing parent styles when ad isn't filled

[csdude55]

I currently have something like this:

<style>
.ad_block {
 display: block;
 padding: 20px 0;
 background: #F5F7F9
}
</style>

<script>
googletag.cmd.push(function() {
 googletag.defineSlot('/12345/foo', ['fluid'], 'ad_block')
  .addService(googletag.pubads());

 googletag.pubads().enableSingleRequest();
 googletag.enableServices();
 googletag.display('ad_block');
});
</script>

This works fine, but when there's no ad available then I end up with a 40px blank spot. Using collapseEmptyDivs() doesn't help either, I guess because the style is on the parent container?

Based on this:
[developers.google.com...]

I discovered that I could do this:

<script>
googletag.cmd.push(function() {
 googletag.defineSlot('/12345/foo', ['fluid'], 'ad_block')
  .addService(googletag.pubads());

 googletag.pubads().enableSingleRequest();

 // this is the new part
 if (googletag.pubads().collapseEmptyDivs())
  console.log('collapsed!');

 googletag.enableServices();
 googletag.display('ad_block');
});
</script>

and I do see "collapsed!" in the console!

But when I change that to document.getElementById('ad_block').style.display = 'none';, nothing is changed. On a 1am hunch I also tried = 'none !important';, but that didn't work either.

Any other thoughts or suggestions?