title: Why Integer doesn't solve null String
body: <p>Integer class contains some method to convert String into Integer:</p>
  
  <ol>
  <li><p><code>Integer.parseInt(null);</code> Parameter: String Return: int, so I expected when parameter is null this throw NPE</p></li>
  <li><p><code>Integer.valueOf(null);</code> Parameter: String Return: Integer,so I expected when parameter is null this should return null. But this precondition was wrong and I ask why there is no such method which can handle this situation ?</p></li>
  </ol>