code: public Set<WeightedDirectedTypedEdge<T>> getEdges(int vertex1, int vertex2, 
                                                Set<T> types) {
          SparseWeightedDirectedTypedEdgeSet<T> edges = vertexToEdges.get(vertex1);        
          return (edges == null) 
              ? Collections.<WeightedDirectedTypedEdge<T>>emptySet()
              : edges.getEdges(vertex2, types);        
      }
docs: {@inheritDoc}