Updating nullable DataTable columns

While NULL is a standard feature and business-as-usual in the SQL world, and likewise null objects are common in the C# world, the concept of NULL and null are completely different things and the translation is easily forgotten. This is particularly important when correlating a data-aware C# object to a SQL database.

Assigning NULL to a C# SqlCommand.SqlParameter, where the column mes_route_step_id allows NULL values:

private static readonly string SQL_Insert =
            "INSERT INTO aca_wip_tracked_steps ( "
            + "route_step_name  "
            + ",mes_route_step_id  "
            + ",aca_wip_tracked_stepgroup_id  "
            + ") "
            + " OUTPUT INSERTED.aca_wip_tracked_step_id "
            + " VALUES "
            + "( "
            + "@route_step_name  "
            + ",@mes_route_step_id  "
            + ",@aca_wip_tracked_stepgroup_id  "
            + ") ";

SqlCommand sc = new SqlCommand();
sc.CommandText = SQL_Insert;
sc.Parameters.Add("@route_step_name", System.Data.SqlDbType.NVarChar, 255).Value
            = _route_step_name;
sc.Parameters.Add("@mes_route_step_id", System.Data.SqlDbType.UniqueIdentifier).Value 
            = _mes_route_step_id.Equals(String.Empty) 
            ? System.Data.SqlTypes.SqlGuid.Null 
            : new Guid(_mes_route_step_id);
sc.Parameters.Add("@aca_wip_tracked_stepgroup_id", System.Data.SqlDbType.UniqueIdentifier).Value 
            = _aca_wip_tracked_stepgroup_id.Equals(String.Empty) 
            ? System.Data.SqlTypes.SqlGuid.Null 
            : new Guid(_aca_wip_tracked_stepgroup_id);

Assigning NULL to the Datatable that correlates to the database:

if (flagInsertingNewRecord)
{
    DataRow row = dt.NewRow();
    row["aca_wip_tracked_step_id"] = insertedID;
    row["route_step_name"] = route_step_name;
    if (mes_route_step_id.Equals(String.Empty))
        row["mes_route_step_id"] = System.DBNull.Value;
    else
        row["mes_route_step_id"] = mes_route_step_id;
    row["aca_wip_tracked_stepgroup_id"] = lblAcaWipTrackedStepGroupId.Text;
    dt.Rows.Add(row);
}
else
{
    for (int row = 0; row < dt.Rows.Count; row++)
    {
        if (dt.Rows[row]["aca_wip_tracked_step_id"].ToString().Equals(insertedID))
        {
            dt.Rows[row]["route_step_name"] = route_step_name;
            if (mes_route_step_id.Equals(String.Empty))
                dt.Rows[row]["mes_route_step_id"] = System.DBNull.Value;
            else
                dt.Rows[row]["mes_route_step_id"] = mes_route_step_id;
            dt.Rows[row]["aca_wip_tracked_stepgroup_id"] = lblAcaWipTrackedStepGroupId.Text;
            break; // early exit of for loop.
        }
    }
}