how to fetch the binded data in coded step with C#

I am creating a test with coded steps using C#. I created a coded step to verify whether the specific column of the binding Exel data sheet is NULL or not.  If it is null, do thing 1. If it is not, do thing 2.
I wanna know that how to fetch the data, I mean , use which method or property.
For example:
string flag;
flag = ?     // flag is the data (column name is "CustomerName") from Exel.  I want to know what i shoud code to replace the "?".
if (flag==" " || flag == null)
   {
         do thing 1;
    }
else
   {
        do thing 2;
   }
 It is urgent. Thank you very much.