Consider My dynamically generated datatable contains the following fileds Id,Name,Mob1,Mob2

If my datatable has this it get inserted successfully,

Id Name Mob1        Mob2
1  acp  9994564564  9568848526

But when it is like this it gets failed saying,

Id Name Mob1        Mob2
1  acp  9994564564  

The given value of type String from the data source cannot be converted to type decimal of the specified target column.

I generating my datatable by readingt a csv file,

    CSVReader reader = new CSVReader(CSVFile.PostedFile.InputStream);
    string[] headers = reader.GetCSVLine();
    DataTable dt = new DataTable();
    foreach (string strHeader in headers)
    {
        dt.Columns.Add(strHeader);
    }
    string[] data;
    while ((data = reader.GetCSVLine()) != null)
    {
        dt.Rows.Add(data);
    }

Any suggestion how to insert null value for numeric field during BulkCopy in c#...

EDIT:

I tried this dt.Columns["Mob2"].AllowDBNull = true; but it doesn't seem to work...