title: updating date to null
body: <p>I am trying to update a enroll_date row to null and it is telling me <code>"cannot update (%s) to NULL"</code>, so I tried doing putting <code>TO_CHAR</code>and it still doesn't help...</p>
  
  <p>enroll_date shows this which I want to make it to null</p>
  
  <pre><code>ENROLL_DATE 
  07-FEB-07  
  </code></pre>
  
  <p>This is what I have</p>
  
  <pre><code>UPDATE ENROLLMENT
  SET TO_CHAR(ENROLL_DATE) = NULL
  WHERE STUDENT_ID ='125'
        AND SECTION_ID ='61';
  </code></pre>
  
  <p>how can I set enroll_date to null ?</p>