[ns] Segmentation fault in Aodv

[st109921]

Hi All

I add something extra in my aodv.cc file like this

void
AODV::rt_update(aodv_rt_entry *rt, u_int32_t seqnum, u_int16_t metric,
                nsaddr_t nexthop, double expire_time) {

     AODV_Neighbor *nb = nb_lookup(nexthop);
         rt->rt_seqno = seqnum;
     rt->rt_hops = metric;
     rt->rt_flags = RTF_UP;
     rt->rt_nexthop = nexthop;
     rt->rt_expire = expire_time;
     // Add Extra
     rt->rt_CITwo = nb->ci_two;

}

when I command make and then run the tcl file like this "ns 20node.tcl"
I got warning that is "segmentation fault".
How can I fix this error?

Thank you