Resolving System.NullReferenceException When Upgrading from ASP.NET 4.8 to ASP.NET Core 6.0

Troubleshoot `System.NullReferenceException` in ASP.NET Core 6.0 with our guide. Learn why your project encounters errors during an upgrade and how to solve them effectively.
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Troubleshooting System.NullReferenceException in ASP.NET Core 6.0

Upgrading a project from ASP.NET Framework to ASP.NET Core can sometimes lead to unforeseen challenges, particularly when it comes to database interactions. A common issue developers encounter is the dreaded System.NullReferenceException. This error typically surfaces when your code tries to use an object that hasn't been instantiated, leading to application crashes. In this post, we will dissect a specific case involving the error and demonstrate a clear pathway to resolution.

The Problem

In the example discussed, a developer faced a System.NullReferenceException while trying to retrieve user data through an OData endpoint. The code that led to the error was a method meant to retrieve data from a database and represented the migration from ASP.NET 4.8 to ASP.NET Core 6.0.

Key Details of the Code

Here’s a brief look at the method that triggered the error:

[[See Video to Reveal this Text or Code Snippet]]

The error appeared on the line where an empty list of User objects was instantiated. This was unexpected, as this code worked fine in ASP.NET 4.8.

Analyzing the Cause

Why Did It Happen?

The Solution: Updating Configuration Access

To solve the issue, you need to ensure that your SQL connection string is properly configured. Here’s how to handle it in ASP.NET Core:

Step 1: Update your Configuration File

Add your connection string as follows:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Modify your UserService Constructor

Instead of using ConfigurationManager, inject the configuration into your service class. Here’s a revised version of the UserService:

[[See Video to Reveal this Text or Code Snippet]]

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Upgrading projects can open doors to new improvements, but they also require a meticulous approach to error handling and configuration. By understanding the nature of System.NullReferenceException and updating your configuration access appropriately, you can ensure a smooth transition to ASP.NET Core 6.0.

If you’re facing a similar dilemma, take heed to validate your configurations diligently and make the necessary adjustments in service registration and injection. Happy coding!