title: Operator '??' cannot be applied to operands of type 'string' and 'System.DBNull'
body: <p>I have the following C# code:</p>
  
  <pre><code>sqlCommand.Parameters.AddWithValue("@Parameter", table.Value ?? DBNull.Value);
  </code></pre>
  
  <p>But it throws the following compilation error:</p>
  
  <blockquote>
    <p>Operator <code>??</code> cannot be applied to operands of type <code>string</code> and <code>System.DBNull</code></p>
  </blockquote>
  
  <p>Why doesn't the compiler allow this syntax?</p>