title: SqlParameter with Nullable value give error while ExecuteNonQuery?
body: <p>I have an sql query that has a parameter that can be null in the database (Sql Server). The update method work fine until that user put a blank in the field, this produce a null value for the DataTime object (this object is nullable). The problem is when the <code>dbCommand.ExecuteNonQuery();</code>.</p>
  
  <p>Here is how I build the parameter for this field:</p>
  
  <pre><code>    IDataParameter dbParam_au_id = new SqlParameter();
      dbParam_au_id.ParameterName = "@birthday";
      dbParam_au_id.Value = birthday;
      dbParam_au_id.DbType = DbType.DateTime;
      dbCommand.Parameters.Add(dbParam_au_id);
  </code></pre>
  
  <p>I have try to convert the null value of birthday to DBNull.Value like that :</p>
  
  <pre><code>    IDataParameter dbParam_au_id = new SqlParameter();
      dbParam_au_id.ParameterName = "@birthday";
      dbParam_au_id.Value = birthday??DBNull.Value;
      dbParam_au_id.DbType = DbType.DateTime;
      dbCommand.Parameters.Add(dbParam_au_id);
  </code></pre>
  
  <p>But this code won't compile and I get error :</p>
  
  <blockquote>
    <p>Error 1   Operator '??' cannot be applied to operands of type 'System.DateTime?' and 'System.DBNull'  </p>
  </blockquote>
  
  <p>Any idea?</p>