title: Oracle VPD column masking, how can I change the default (null) value to XXX
body: <p>Using Oracle VPD, after adding a policy and creating a function, I was able to hide a column from unauthorized users.</p>
  
  <p>But instead of (null) how can i show something like 'xxxxxx'</p>
  
  <p>Also in the function I am validation for the user login, like</p>
  
  <pre><code>if sys_context( 'userenv', 'session_user' ) = 'USER1'
  </code></pre>
  
  <p>what is the best approach to remove this hard coding in the function?</p>
  
  <p>Thanks in advance.</p>