---

This section details on the original issue you should resolve

<issue_title>The WriteOnceBlock method ReceiveAsnyc returns null instead of value passed in Post method</issue_title>
<issue_description>### Description

I discovered that the instance of WriteOnceBlock<T> when used to pass a value between two tasks with Post and ReceiveAsnyc methods doesn't work as expected. Sometimes when a value is written to WriteOnceBlock<T> with Post method, ReceiveAsync method reads null instead of value used in Post.

After Post(someObject) is called i expect that await writeOnceBlock.ReceiveAsync() is evaluated to someObject.

Instead i get null.

Reproduction Steps

using System.Threading.Tasks.Dataflow;

Console.WriteLine("Start");
int i = 0;
while (true)
{
    if (i == 100_000)
        break;
    var wo = new WriteOnceBlock<object>(a => a);
    var t1 = Task.Run(() =>
    {
        wo.Post(new object());
    });
    var t2 = Task.Run(async () =>
    {
        var o = await wo.ReceiveAsync();
        if (o == null)
        {
            Console.WriteLine("object is null 1");

            o = await wo.ReceiveAsync();
            if (o == null)
                Console.WriteLine("object is null 2");
        }
    });

    await t1;
    await t2;
    i++;
}
Console.WriteLine("End");

Expected behavior

Start
End

Actual behavior

Start
object is null 1
object is null 1
object is null 1
object is null 1
End

Regression?

/

Known Workarounds

If null is returned, calling ReceiveAsync again will get a value instead of null.

Configuration

.NET 8.0
Windows 11
64-bit operating system, x64-based processor

Other information

I think it might be some kind of synchronization issue.</issue_description>

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