Server error, object reference not set to an instance of an object. Everyone can help me please

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Server Error in '/' Application.
Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

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

Source Error:


Line 36: 
Line 37:         Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Line 38:             DocType.Text = Session("docType").ToString()

What I have tried:

I need to solve it, the source error is in line 38 I try to fix for two days but without goal

Posted 26-Jul-21 2:27am

Rodolfo Olivieri 2021

Updated 26-Jul-21 3:29am

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Richard MacCutchan 26-Jul-21 9:28am

Either DocType has not been initialised, or Session does not contain a property named "docType"

2 solutions

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OriginalGriff · Answer 1 · 2021-07-26T03:08:00

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterday's shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, it will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, the debugger will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!

Dave Kreskowiak · Answer 2 · 2021-07-26T03:29:00

Solution 2

Simple. Your code is assuming that Session("docType") returned an object, but it didn't. Apparently, somewhere else in your code, you never set a value in the Session object with a label of "docType".

Posted 26-Jul-21 3:29am

Dave Kreskowiak