title: Search query for empty\null string field in Azure search
body: <p>Hi I have a string field which can be empty\null for certain documents. I like to know how to search for  those documents.</p>
  
  <p>I want to know thru searchquery and not ODatFilter as I may like to solve following cases:</p>
  
  <ol>
  <li>searching for empty\null in this field A</li>
  <li>searching for substring in this field A( Eg: A:test)</li>
  <li>searching for both empty\null or values containing test.</li>
  </ol>
  
  <p>So ODataFilter suggestions will not help in achieving #2 so #1 should be using searchQuery.</p>
  
  <p>Any help is appreciated.</p>