title: Check for DbNull in C#
body: <p>I am finding difficulties in validating the following </p>
  
  <pre><code>if(personDS.person[0].IdFk!= DBNull.Value)
  </code></pre>
  
  <p>this is the compile time error - cannot be applied to operands of type 'System.Guid and 'System.Dbnull'</p>