使用C＃的ASP.NET中的NullReferenceException错误 - 尝试处理错误

I have a ASP.NET webform that, aside from other controls, has a textbox for entering a value, a textbox to display values, a dropdownlistbox, and a search button. I am using the following code to display search results:I have a ASP.NET webform that, aside from other