title: Handle columns with NULL values with SuperCSV
body: <p>Is there a way to configure how SuperCSV expects to handle NULL values?  This is sometimes handled as:</p>
  
  <pre><code>,,
  </code></pre>
  
  <p>or as:</p>
  
  <pre><code>,NULL,
  </code></pre>
  
  <p>or as:</p>
  
  <pre><code>,null,
  </code></pre>
  
  <p>But I can't seem to find a way to configure how SuperCSV expects to handle these, especially for numeric columns.</p>