DataSource Controls :: NULL Value Returned From Database And Handling It

I'm developing a website using asp.net 2.0 . I have retrieved a record from database through the query.

SqlConnection con = new SqlConnection(connectionstring);
con.Open();
String SQL = "SELECT * FROM Table where attribute1 = value";
SqlCommand cmd = new SqlCommand(SQL, con);
SqlDataReader reader = cmd.ExecuteReader();

Sometimes, there is no record matching this query and so null value is retrieved. My question is how to find that the null value is returned. Since If (no record found i.e NULL) certain actions needs to be done and if (records found i.e NOT NULL) ceratin different actions needs to be carried out.