C#中DBNull问题

/// 

        /// 插入数据
        /// 
        /// 
        /// 
        private void button2_Click(object sender, RoutedEventArgs e)
        {
            string name = txtName.Text;
            string age = txtAge.Text;
            string height = txtHeight.Text;
            object objName;
            if (name.Length <= 0)
            {
                objName = DBNull.Value;
            }
            else
            {
                objName = name;
            }
            object objAge;
            if (age.Length <= 0)
            {
                objAge = DBNull.Value;
            }
            else
            {
                objAge = age;
            }
            object objHeight;
            if (height.Length <= 0)
            {
                objHeight = DBNull.Value;
            }
            else
            {
                objHeight = height;
            }
            SqlHelper.ExecuteNonQuery(@"insert into T_Person(Name,Age,Height) values (@Name,@Age,@Height)",
                new SqlParameter("@Name", objName),
                new SqlParameter("@Age", objAge),
                new SqlParameter("@Height", objHeight));
        }
        /// 

        /// 读出数据
        /// 
        /// 
        /// 
        private void button3_Click(object sender, RoutedEventArgs e)
        {
            DataSet ds = SqlHelper.ExecuteDataSet("select * from T_Person where id=2");

            string name;
            if (ds.Tables[0].Rows[0]["Name"] == DBNull.Value)
            {
                name = null;
            }
            else
            {
                name = ds.Tables[0].Rows[0]["Name"].ToString();
            }
            int? age;
            if (ds.Tables[0].Rows[0]["Age"] == DBNull.Value)
            {
                age = null;
            }
            else
            {
                age = int.Parse(ds.Tables[0].Rows[0]["Age"].ToString());
            }
            txtName.Text = name;
            txtAge.Text = age.ToString();
            txtHeight.Text=ds.Tables[0].Rows[0]["Height"].ToString();
        }