Unexpected NullReferenceException when using LINQ with GroupBy on a Nullable Property in C# 10
Could someone explain I'm relatively new to this, so bear with me. I'm working with a `NullReferenceException` when trying to group a list of objects by a nullable property using LINQ in C# 10. The list contains several objects where the grouping key can be null, and I'm unsure why this is happening. Here’s the simplified version of my code: ```csharp public class Product { public int Id { get; set; } public string Name { get; set; } public int? CategoryId { get; set; } } List<Product> products = new List<Product> { new Product { Id = 1, Name = "Product A", CategoryId = 1 }, new Product { Id = 2, Name = "Product B", CategoryId = null }, new Product { Id = 3, Name = "Product C", CategoryId = 2 }, }; var groupedProducts = products.GroupBy(p => p.CategoryId); ``` When I run this code, I get the following behavior: ``` NullReferenceException: Object reference not set to an instance of an object. ``` I tried checking if `CategoryId` is null before grouping, but that seems cumbersome and does not solve the question. I would expect the grouping to handle null values gracefully and create a group for those products without a category. I've also verified that the `products` list is properly instantiated and populated before the grouping operation. Can anyone guide to understand why this exception is occurring and how I can handle grouping by a nullable property correctly? Thanks for any help you can provide! I'm working on a REST API that needs to handle this. I'd be grateful for any help. I've been using C# for about a year now. Thanks for taking the time to read this!