Any function in List raised "Null Reference" exception.

[SMAH1]

Description

Hi
I use xUnit for unit test.
I have "Async" method add item to List.
To avoid repeating a key, I use the Any function in the List.
I rarely get a Null Reference exception when running tests.
I can't reproduce this error every time, but I've seen it rarely.

Reproduction Steps

I can't reproduce this error every time, but I've seen it rarely.

Expected behavior

The list has data. Why should it give a no data error when executing linq?

Actual behavior

Run Any method correctly.

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

OS: Windows 22H2 (19042.4529).
.NET core:

6.0.425 [C:\Program Files\dotnet\sdk]
7.0.410 [C:\Program Files\dotnet\sdk]
8.0.206 [C:\Program Files\dotnet\sdk]
9.0.102 [C:\Program Files\dotnet\sdk]

Microsoft Visual Studio Community 2022 (64-bit) Version 17.12.4

[Tornhoof]

Why an async method for that?
Where do you await the Task?
List is not threadsafe to Insert, so it's likely you do something concurrently with it outside of the screenshot.

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[huoyaoyuan]

Concurrent access of List<T> is incorrect. To gather a few items into a list, running in single thread is much more efficient. To gather a huge number of items by utilizing multiple threads, PLINQ is the convenient solution.

Closing as answered.