C# Association attribute not understood

SonarQube is incorrectly reporting an error in the following code:

private readonly EntitySet _DataItems = new EntitySet();
[Association(Name = “DataItems”, Storage = “_DataItems”, ThisKey = “Id”, OtherKey = “OtherId”
public ICollection DataItems
{
get => _DataItems;
set => _DataItems.Assign(value);
}

saying that the ‘set’ statement needs to refer directly to _DataItems. This is wrong. Doing so would result in a compile error