Not a solution to your question, but another problem you have.
Never build an SQL query by concatenating strings. Sooner or later, you will do it with user inputs, and this opens door to a vulnerability named "SQL injection", it is dangerous for your database and error prone.
A single quote in a name and your program crash. If a user input a name like "Brian O'Conner" can crash your app, it is an SQL injection vulnerability, and the crash is the least of the problems, a malicious user input and it is promoted to SQL commands with all credentials.
SQL injection - Wikipedia[
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SQL Injection[
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Quote:
Object reference not set to an instance of an object!
Use the debugger to see where is the error and check the variables, 1 of them is not what is expected. The command that is supposed to set that object have failed, but you don't know until you try to use it.
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There is a tool that allow you to see what your code is doing, its name is
debugger. It is also a great learning tool because it show you reality and you can see which expectation match reality.
When you don't understand what your code is doing or why it does what it does, the answer is
debugger.
Use the debugger 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[
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Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[
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Basic Debugging with Visual Studio 2010 - YouTube[
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Visual Basic / Visual Studio Video Tutorial - Basic Debugging - YouTube[
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Visual Basic .NET programming for Beginners - Breakpoints and Debugging Tools[
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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 find bugs, it just help you to. When the code don't do what is expected, you are close to a bug.