DBNull assign to a sqlparameter? http://stackoverflow.com/questions/4555935/how-to-assign-null-to-a-sqlparameter

DBNull

SqlParameter[] parameters = new SqlParameter[1];     
SqlParameter planIndexParameter = new SqlParameter("@AgeIndex", SqlDbType.Int);
planIndexParameter.Value = (object)AgeItem.AgeIndex ?? DBNull.Value;
parameters[0] = planIndexParameter; 

...

if (AgeItem.AgeIndex== null)
    planIndexParameter.Value = DBNull.Value;
else
    planIndexParameter.Value = AgeItem.AgeIndex;
    
...

foreach (SqlParameter parameter in sqlCmd.Parameters)
{
    if (parameter.Value == null)
    {
        parameter.Value = DBNull.Value;
    }
}