<value>The EnumeratorCancellationAttribute applied to parameter '{0}' will have no effect. The attribute is only effective on a parameter of type CancellationToken in an async-iterator method returning IAsyncEnumerable</value>
// (27,32): warning CS8634: The type 'T?' cannot be used as type parameter 'T' in the generic type or method 'S<T>'. Nullability of type argument 'T?' doesn't match 'class' constraint.