I came across a bug in Rhino.Geometry.Intersect.Intersection.MeshMeshFast(). I am getting the error message
Message: Value cannot be null.
Parameter name: source
I believe that the Intersection.MeshMeshFast() function first calls the new Intersection.MeshMesh() function to set the Polyline source, and on failure returns null. However, the Intersection.MeshMesh() function can complete successfully and return Polyline intersections as null. This then causes the error in Intersection.MeshMeshFast() without it being able to call UnsafeNativeMethods.ON_Mesh_IntersectMesh(). Should be quick to fix.