title: Why nullable int (int?) doesn't increase the value via "+=" if the value is NULL?
body: <p>I have a page counter type of int?:</p>
  
  <pre><code>spot.ViewCount += 1;
  </code></pre>
  
  <p>It works ONLY if the value of ViewCount property is <strong>NOT NULL</strong> (any int).</p>
  
  <p>Why the compiler do so?</p>
  
  <p>I would be grateful for any solutions.</p>