sql - how to check for null in datarow row in c# -

i have code

  foreach (datarow row in dtgraph.rows)             {                 string username = row["username"].tostring();                 string loggedstate = row["loggedstate"].tostring();                 string interactionid = row["interactionid"].tostring();                 string interactiontype = row["interactiontype"].tostring();              } 

how check if row["something"] null?

i tried run code, , null values becomes "" (empty).

i need check if these null.

i stupid question, problem making tostring() thought null becomes null or null or null or empty?

thanks

use dbnull.value

 var username = row["username"].tostring(); 

to

 var username =  reader["username"] != dbnull.value ? row["username"].tostring():""; 

update

 var username = "";  if(reader["username"] != dbnull.value)  {      username = row["username"].tostring();  }