Feature request

IMHO The join type should be left when the reference field is optional/nullable, for example:

[Reference(typeof(SCollection), ReferenceAttribute.JoinType.Left)]
public SCollection? Collection { get; set; }

Describe the solution you'd like

I'm pretty new to C# so I'm not sure if this is possible, I would say that you cannot do this with Java annotations.

If this is possible, I don't mind to learn how annotations work in C# and help with this change.