Wot no key?

Wot no key? (Allow principal/dependent to be flipped by specifying FK type only)

Allows the ForeignKey API to be used without any parameters to specify/flip the principal and dependent while the FK property itself is still discovered by convention.
This doesn't look very clear to me. A couple of reasons that pop to mind:

1. `ForeignKey<Product>()` per se doesn't seem to mean that the foreign key is on product: in the overload that takes an actual property access the generic argument is there to provide the starting point, but if you just remove the property access it doesn't quite work in the same way.
2. My first intuition when looking at this overload is that the empty parenthesis are at the same time asserting that the FK isn't present in the CLR type, i.e. that it overrides the convention. 

I understand that I might just need to adjust my mental model but I would still want to discuss this and hear what others think.