title: how to fix PHP Notice: Undefined index (don't show 'what's file error')
body: <p>I got too many for this warning debug in wordpress ver 4.2.4
  but they didnt showed which file gave this warning.</p>
  
  <p><code>debug.log</code> show only this message.</p>
  
  <pre><code>PHP Notice:  Undefined offset: 4
  PHP Notice:  Undefined index: 36
  PHP Notice:  Undefined property: stdClass::$unread
  PHP Notice:  Undefined index: topicname
  </code></pre>
  
  <p>How can I find and fix this warning?</p>