-xbt_dict_t traces_set_list = NULL;
-XBT_PRIVATE xbt_dict_t trace_connect_list_host_avail = NULL;
-XBT_PRIVATE xbt_dict_t trace_connect_list_host_speed = NULL;
-XBT_PRIVATE xbt_dict_t trace_connect_list_link_avail = NULL;
-XBT_PRIVATE xbt_dict_t trace_connect_list_link_bw = NULL;
-XBT_PRIVATE xbt_dict_t trace_connect_list_link_lat = NULL;
+xbt_dict_t traces_set_list = nullptr;
+XBT_PRIVATE xbt_dict_t trace_connect_list_host_avail = nullptr;
+XBT_PRIVATE xbt_dict_t trace_connect_list_host_speed = nullptr;
+XBT_PRIVATE xbt_dict_t trace_connect_list_link_avail = nullptr;
+XBT_PRIVATE xbt_dict_t trace_connect_list_link_bw = nullptr;
+XBT_PRIVATE xbt_dict_t trace_connect_list_link_lat = nullptr;