title: Remove or set Document Query Language attribute to null
body: <p>Could someone please help me with this? I am trying to get rid of the ATTRIBUTE "effective_date" or set it to null date by using the below 2 queries and am getting different errors.</p>
  
  <pre><code>=====================================
  UPDATE 
      cd_quality (ALL) OBJECTS
  TRUNCATE
      effective_date
  WHERE
      FOLDER ('C:/temp/path')
  AND
      object_name = 'ab'
  </code></pre>
  
  <p>...</p>
  
  <pre><code>[DM_QUERY_E_UP_SINGLE]error:  "The attribute effective_date is a single-valued attribute."
  
  ===============================
  UPDATE
      cd_quality(all) objects 
  SET
      effective_date = ''
  WHERE
      FOLDER ('C:/temp/path')
  AND 
      object_name = 'ab'
  
  ...
  [DM_QUERY_E_UP_CHAR]error:  "UPDATE:  You have attempted to set a non-string attribute (effective_date) with a string value ()."
  </code></pre>
  
  <p>I also tried the second query with: Set effective_date = null
  But it still didn’t work. Is there a different null value for dates? </p>