docs: static <S, E1, E2> GraphTraversal<S, E2> union(
              GraphTraversal<S, ? extends E1> start, Iterable<GraphTraversal<? super E1, ? extends E2>> traversals) {
          // This is safe, because we know all the arguments are of the right type
          //noinspection unchecked
          GraphTraversal<E1, E2>[] array = (GraphTraversal<E1, E2>[]) Iterables.toArray(traversals, GraphTraversal.class);
  
          return start.union(array);
      }