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

In asp.net development, you encounter a System.NullReferenceException: An error prompt that does not set an object reference to an instance of an object is resolved as follows:

(1) The variable being set is NULL or does not have a value, typically occurs when passing parameters, and also occurs when using data controls such as the DataGrid or GridView or DataList.
(2) The control name does not correspond to the codebehind inside
(3) Initialization of object not with new
(4) The control referenced in the program does not exist
Workaround:
(1) Use Try ... Catch...finally catch the error, or output the variable value directly with Response.Write ()
(2) To see if there are any uninitialized variables in the code