how do i solve the System.NullReferenceException error

System.NullReferenceException: Object reference not set to an instance of an object

String sql, connection, lname, fileloc;
           sql = "select FileLoc, Fname, Lname from apps where Lname = '"+searchString.Text+"'";
           connection = Properties.Settings.Default.cvmanagerConnectionString;

           SqlDataReader reader = null;

           SqlConnection conn = new SqlConnection(connection);
           SqlCommand cmd = new SqlCommand(sql, conn);

           try
           {
               conn.Open();
               cmd.ExecuteReader();

               intsearchLB.Enabled = true;

               while (reader.Read())// THIS IS LINE 39
               {
                   lname = reader["Lname"].ToString();
                   fileloc = reader["FileLoc"].ToString();

                   intsearchLB.Items.Add(new searchresults(lname, fileloc));
               }

           }
           catch (Exception ex)
           {
               MessageBox.Show(ex.ToString());
           }
           finally
           {
               nsCancel.Enabled = true;
               nsView.Enabled = true;
               nsEdit.Enabled = true;
               nsSave.Enabled = true;
               nsDate.Enabled = true;
               nsTime.Enabled = true;
           }