Adapted comment

core/net/rpl/rpl-dag.c

@@ -703,8 +703,8 @@ rpl_remove_parent(rpl_dag_t *dag, rpl_parent_t *parent)
 void
 rpl_nullify_parent(rpl_dag_t *dag, rpl_parent_t *parent)
 {
-  // local repair calls nullification because the preferred parent is NULL!
-  // So check if parent is NULL to trigger uip_ds6_defrt_rm.
+  /* This function can be called when the preferred parent is NULL, so we
+     need to handle this condition in order to trigger uip_ds6_defrt_rm. */
   if(parent == dag->preferred_parent || dag->preferred_parent == NULL) {
     dag->preferred_parent = NULL;
     dag->rank = INFINITE_RANK;