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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:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
Money_Changer.Cusinfo.BtnSave_Click(Object sender, EventArgs e) in C:\Users\Zeeyana\source\repos\Money Changer\Money Changer\Cusinfo.aspx.cs:138
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +9782310
System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +204
System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +12
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +15
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +35
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1639

What I have tried:

<add name="ConnectionString" connectionstring="Data Source=;Initial Catalog=mccisdatabase;Integrated Security=False;User ID=myuname;Password=pw" providername="System.Data.SqlClient">
Updated 24-Jul-19 13:49pm
raddevus 21-Jul-19 18:26pm
What is on line 138 of Cusinfo.aspx.cs?
C:\Users\Zeeyana\source\repos\Money Changer\Money Changer\Cusinfo.aspx.cs:138

That is the thing that the runtime thinks is null.
Darwin Ahmed 21-Jul-19 19:54pm
Cusinfo.aspx.cs is my file in my local machine and there is none in my code like that, but it appears when error occurred.

In my local machine, there is no problem, but on my domain, when i try to save data to database, that error appears.

Richard MacCutchan 22-Jul-19 3:43am
Most likely because that address is not valid when the code is running in the server. You need to change the Data Source location to a valid server address.
Darwin Ahmed 22-Jul-19 7:48am
datasource is valid, because i have login page in my website and verified my username and password to database, but when i use data entry and save, error occur.
Richard MacCutchan 22-Jul-19 11:16am
Then as noted below, you need to investigate which variable is null. We cannot do it as we have no access to your system.

The error is clearly at C:\Users\Zeeyana\source\repos\Money Changer\Money Changer\Cusinfo.aspx.cs:138 so that is where to start looking.

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 yesterdays 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, VS 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, VS 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!
This is a very, very, easy problem to solve and only you can do it since we can't run your code. You are trying to access something that is null. Debug your code and you'll find it right away. Simple.
We can't workout anything beyond the obvious from this.
Somewhere in your code, there is a fail and an operation return nothing instead of expected object. When you try to use the object, you get the error.

Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your code is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

Debugging C# Code in Visual Studio - YouTube[^]

The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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