title: Handling NULL values in DAX Query to get distinct Items from multiple Tables
body: <pre><code>TravelCategory = DISTINCT(UNION(VALUES('CrossCutting'[Travel_Category]), VALUES( 'EntitlementTravel'[Travel_Category]), VALUES( 'HRTravel'[Travel_Category]),VALUES( 'OfficialTravel'[Travel_Category]))) 
  </code></pre>
  
  <p>I have the above table which gives me a distinct list of <strong>Travel_Category</strong> from 4 different tables. </p>
  
  <p>How can i set a default value if the <strong>Travel_Category</strong> is NULL for a row in any of the tables above?</p>