#nullable enable

class C<T> where T : notnull
{
    void M(T initial, System.Func<T, T?> selector)
    {
        // ⚠ CS8600 Converting null literal or possible null value to non-nullable type.
        //                                                     ↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓
        for (var current = initial; current != null; current = selector(current))
        {
        }
    }
}