#vulnerable code 
                             public void printConnectivity() {
		Iterator<GraphicNode> keys = connectivity.keySet().iterator();

		System.err.printf("Graphic graph connectivity:%n");

		while (keys.hasNext()) {
			GraphicNode node = keys.next();
			System.err.printf("    [%s] -> ", node.getId());
			ArrayList<GraphicEdge> edges = connectivity.get(node);
			for (GraphicEdge edge : edges)
				System.err.printf(" (%s %d)", edge.getId(),
						edge.getMultiIndex());
			System.err.printf("%n");
		}
	} 
                            #location 10 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             public void printConnectivity() {
		Iterator<GraphicNode> keys = connectivity.keySet().iterator();

		System.err.printf("Graphic graph connectivity:%n");

		while (keys.hasNext()) {
			GraphicNode node = keys.next();
			System.err.printf("    [%s] -> ", node.getId());
			Iterable<GraphicEdge> edges = connectivity.get(node);
			for (GraphicEdge edge : edges)
				System.err.printf(" (%s %d)", edge.getId(),
						edge.getMultiIndex());
			System.err.printf("%n");
		}
	}