title: Custom number format for NULL
body: <p>I have an excel sheet that I populate from a database. What is the custom number format that I can use to replace NULL values in the excel by a hyphen '-' ?
  I know that I can use the following formula</p>
  
  <pre><code>#,##0_);(#,##0);–_);_(@_)
  </code></pre>
  
  <p>in order to display it for a zero. But I don't know how to handle a null value.</p>