yield return null;

In C#, the statement "yield return null;" is used in an iterator block to yield null as the current value of the iterator. It is commonly used to indicate the end of the sequence or to represent a null value in the sequence.

Here is an example of how it can be used in an iterator block:

public IEnumerable<string> GetNames()
{
    yield return "John";
    yield return "Jane";
    yield return null;
    yield return "Mike";
}

var names = GetNames();
foreach (var name in names)
{
    if (name == null)
    {
        Console.WriteLine("Null value found");
    }
    else
    {
        Console.WriteLine(name);
    }
}

The output of this code would be:

John
Jane
Null value found
Mike
``