Intermittent 'Object reference not set to an instance of an object' While Accessing Properties in a Custom C# Collection
I'm getting frustrated with I need some guidance on After trying multiple solutions online, I still can't figure this out. I'm working with an intermittent `Object reference not set to an instance of an object` behavior when trying to access properties of objects in a custom collection class that implements `IEnumerable<T>`. My collection class is designed to hold a list of custom `User` objects, and I am adding and retrieving users in various parts of my application. However, in some cases, when I try to access a property of a `User` instance, I get this behavior. Here’s a simplified version of my `User` and `UserCollection` classes: ```csharp public class User { public string Name { get; set; } public int Age { get; set; } } public class UserCollection : IEnumerable<User> { private List<User> users = new List<User>(); public void AddUser(User user) { users.Add(user); } public IEnumerator<User> GetEnumerator() { return users.GetEnumerator(); } IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); } } ``` In my application, I’m adding users like this: ```csharp var userCollection = new UserCollection(); userCollection.AddUser(new User { Name = "Alice", Age = 30 }); userCollection.AddUser(new User { Name = "Bob", Age = 25 }); ``` And when I try to access a user like this: ```csharp foreach (var user in userCollection) { Console.WriteLine(user.Name); } ``` In most cases, it works fine, but occasionally I get the `Object reference not set to an instance of an object` behavior. I suspect it might be related to multithreading since I'm accessing the collection from different threads without any synchronization. I’ve tried using a `lock` around the `AddUser` method, but it hasn’t resolved the scenario completely. I also checked for any null references in my `User` objects before adding them, but that doesn’t seem to be the scenario. Could this be a question with how I’m managing the state of the collection or a threading scenario? Has anyone faced a similar question or have suggestions on how to debug this effectively? Any help would be greatly appreciated! Is this even possible? Any pointers in the right direction?