if (myReader["Additional"] != null)
{
    ltlAdditional.Text = "contains data";
}
else
{
     ltlAdditional.Text = "is null";
}

if (myReader["Additional"] != DBNull.Value)
{
    ltlAdditional.Text = "contains data";
}
else
{
     ltlAdditional.Text = "is null";
}

SELECT ISNULL([Additional], -1) AS [Additional]

public static class DataReaderExtensions
{
    public static bool IsDBNull( this IDataReader dataReader, string columnName )
    {
        return dataReader[columnName] == DBNull.Value;
    }
}

DataTable dt = new DataTable();
dt.Rows[0].Table.Columns.Contains("SampleColumn");

if (myReader.Read())
{

    ltlAdditional.Text = "Contains data";
}
else
{
    ltlAdditional.Text = "Is null";
}