Graph is updated. Null pointer exception is fixed

src/main/java/Algorithm/Graph.java

@@ -45,7 +45,7 @@ public class Graph {
 	}
 
 	public int addVertex (String vertex) {
-		if (vertexIndex.containsKey(vertex) == false) {
+		if (!vertexIndex.containsKey(vertex)) {
 			this.vertices.add(numberOfVertices) ;
 			this.vertexIndex.put(vertex, numberOfVertices++) ;
 			this.AdjList.add(new HashSet<>()) ;
@@ -54,7 +54,10 @@ public class Graph {
 	}
 
 	public Graph(String args) {
-		AdjList = new ArrayList<>();
+		this.AdjList = new ArrayList<>();
+		this.vertexIndex = new HashMap<>() ;
+		this.numberOfVertices = 0 ;
+		this.vertices = new ArrayList<>() ;
 		trianglecount = new HashMap<>();
 		try {
 			BufferedReader br = new BufferedReader(new FileReader(args));