title: Should null elements be stored in Cosmos DB or should they be ignored?
body: <p>Is there a good reason to serialize null elements in a Cosmos DB document or is it better to ignore them?</p>
  
  <p>With the is_defined function I can query for undefined elements similar to how I query for null elements.</p>
  
  <p>Does either consume less RUs? In my tests they seem to perform similarly.</p>