Not going inside if statement to return false

public bool changeSession(string sess)
        {

            try
            {
                int i, j;
                string session = sess;
                string qrstr1;// to check whether session which is selected was previous selected or not?
                qrstr1 = "select session from session";
                SqlCommand cmd1 = new SqlCommand(qrstr1, Gencon);
                SqlDataAdapter da = new SqlDataAdapter(cmd1);
                DataTable dt = new DataTable();
                da.Fill(dt);
                for (i = 0; i < dt.Rows.Count; i++)
                    for (j = 0; j < dt.Columns.Count; j++)
                    {
                        object o = dt.Rows[i].ItemArray[j];
                        //string s = dt.Rows[i].ItemArray[j].ToString();
                        string s = o.ToString();
                        if (s.Equals(session))
                        {

                            return false;
                            
                            
                        }
                            

                    }
                            
                    string qrstr;
                    qrstr = "update session set session=@sess where id=@id";
                    SqlCommand cmd = new SqlCommand(qrstr, Gencon);
                    cmd.Parameters.AddWithValue("@id", 1);
                    cmd.Parameters.AddWithValue("@sess", sess);
                    Gencon.Open();
                    cmd.ExecuteNonQuery();
                    Gencon.Close();
                    return true;
                
            }
            catch (Exception ex)
            {
                return false;
            }

        }