#fixed code
                                @Override
    public void addLink(final long srcId, final long destId, final double bandwidth, final double latency) {
        if (getTopologycalGraph() == null) {
            graph = new TopologicalGraph();
        }

        if (entitiesMap == null) {
            entitiesMap = new HashMap<>();
        }

        // maybe add the nodes
        addNodeMapping(srcId);
        addNodeMapping(destId);

        // generate a new link
        getTopologycalGraph().addLink(new TopologicalLink(entitiesMap.get(srcId), entitiesMap.get(destId), (float) latency, (float) bandwidth));

        generateMatrices();
    }
#vulnerable code 
                                @Override
    public void addLink(final long srcId, final long destId, final double bandwidth, final double latency) {
        if (getTopologycalGraph() == null) {
            graph = new TopologicalGraph();
        }

        if (map == null) {
            map = new HashMap<>();
        }

        // maybe add the nodes
        addNodeMapping(srcId);
        addNodeMapping(destId);

        // generate a new link
        getTopologycalGraph().addLink(new TopologicalLink(map.get(srcId), map.get(destId), (float) latency, (float) bandwidth));

        generateMatrices();
    } 
                            #location 16 
                            #vulnerability type NULL_DEREFERENCE