title: writing null to DataOutput in Hadoop
body: <p>I'm using Hadoop 0.20.2. I am writing an object <code>X</code> which implements <code>Writable</code>.</p>
  
  <p><code>X</code> has several fields which are instances of <code>Integer</code>. For these fields, the <code>null</code> value has a special significance.</p>
  
  <p>When serializing the object, by writing to <code>DataOutput out</code> in the <code>write</code> method of the <code>Writable</code> interface, is there a way I can write <code>null</code>? Or should I use separate booleans which indicates the value is null?</p>