title: DateTime.hasvalue vs datetime == null, which one is better and why
body: <p>i'd like to ask a question about <strong>controlling null value</strong> of a datetime.</p>
  
  <pre><code>if (mydatetime != null)
  </code></pre>
  
  <p>or</p>
  
  <pre><code>if(mydatetime.hasvalue)
  </code></pre>
  
  <p>which one is better, or proper and why?</p>
  
  <p>thank you.</p>