Null values -where do they come from
Assuming you're using Views - [noticed the tag]! You're definitively on the right track! Drupal Views integration is an extremely powerful way to get more out of your CiviCRM (literally!).

So to handle this add a Filter in Views to not display such NULL results. Here's an example where I want to make sure that addresses without a Latitude or Longitude do NOT get plotted on a Map: