Right how i use very strange way to check that vertexes adjacency:
val edge = Edge(from, to, null)
return from.adjacency.contains(edge) && to.adjacency.contains(edge)
- so i create edge and check contains, but what important - i have overloaded method equals that allow me to do this thing.
but, it not the best idea to have null for edge weight, and i search way to avoid it