I just encountered a problem with LineLine intersection method with two nearly parallel lines.
Rhino.Geometry.Intersect.Intersection.LineLine(edge1, edge2, out double t1, out double t2)
I was expecting the method return false or the parameters t1 and t2 are out of bounds, But this is not happening. I managed to solve this by a parallel check before computing the intersection.
Just so that you know!