Implementing neighbour discovery in a Unetagent

Question

I have been trying to implement neighbour discovery in a unetagent. This is the code that I have come up with so far:

@Override
    protected void setup() {
        this.nodeList = new ArrayList<>();
        this.currentNodeIndex = 0;

        this.register(Services.MAC);
        this.register(Services.DATAGRAM);
        this.register(Services.ROUTE_MAINTENANCE);
        this.phy = this.agentForService(Services.PHYSICAL);
    }

    @Override
    protected void startup() {
        if (this.phy == null) {
            this.phy = this.agentForService(Services.PHYSICAL);
        }

        if (this.phy == null) {
            this.log.warning("No PHY found, carrier sensing disabled!");
        }

        this.subscribe(this.topic(this.phy, "snoop"));
        // Discover other nodes in the network
        discoverNodes();
    }

    private void discoverNodes() {
        int attempts = 2; // try only a single attempt at discovery
        int phantom = 132; // non-existent node address
        int timeout = 10000; // 10 second timeout

        AgentID rdp = agentForService(Services.ROUTE_MAINTENANCE);
        this.subscribe(this.topic(rdp));

        AgentID datagram = agentForService(org.arl.unet.Services.DATAGRAM);
        this.subscribe(this.topic(datagram));

        RouteDiscoveryReq l = new org.arl.unet.net.RouteDiscoveryReq(phantom);
        l.setCount(attempts);

        rdp.send(l);
        Message ntf;

        while ((ntf = receive(org.arl.unet.net.RouteDiscoveryNtf.class, timeout)) != null) {
            this.log.warning("  Discovered neighbor: " + ((RouteDiscoveryNtf) ntf).getNextHop());
            nodeList.add(((RouteDiscoveryNtf) ntf).getNextHop());
        }

        nodeList = nodeList.stream().distinct().collect(Collectors.toList());
        this.log.warning("Neighbors are " + nodeList);
        NUM_NODES = nodeList.size();
    }

When I try to run the code on my agents it gives me an error that the "mac reservation request was denied: null"

I tried registering all the relevant services to the unetagent but am not able to figure out what the issue seems to be.

When I run the code from a separate .groovy script file on the shell then it works perfectly fine showing the neighbours of the node.

Is there something wrong with my code or am I missing something? Also would it be easier to implement this using a different technique?