public Node GetNode(string id, string type)
            {
                string key = NodeDependencyLookupUtility.GetNodeKey(id, type);

                if (_lookup.ContainsKey(key))
                {
                    return(_lookup[key]);
                }

                return(null);
            }
            private static Node GetOrCreateNode(string id, string type, Dictionary <string, Node> nodeDictionary)
            {
                string key = NodeDependencyLookupUtility.GetNodeKey(id, type);

                if (!nodeDictionary.ContainsKey(key))
                {
                    nodeDictionary.Add(key, new Node {
                        Id = id, Type = type
                    });
                }

                return(nodeDictionary[key]);
            }