[lwip-users] about lwip_close() problem???

[xcb]

lwip-users

        sock=socket();
        connect(); //connect an unreach IP ,it retrun -1;
        close(sock); //problem happen.

lwip_close()->netconn_delete(sock->conn)-> it call:

if (conn->recvmbox != SYS_MBOX_NULL) {
    while (sys_arch_mbox_fetch(conn->recvmbox, &mem, 1) != SYS_ARCH_TIMEOUT) {
      if (conn->type == NETCONN_TCP) {
  pbuf_free((struct pbuf *)mem);        //assert happen
      } else {
  netbuf_delete((struct netbuf *)mem);
      }
    }


mem==NULL;//err_tcp(void *arg, err_t err) -> sys_mbox_post(conn->recvmbox, 
NULL);
now pbuf_free((struct pbuf *)mem),will cause Assertion "p != NULL" failed at 
line 554 in E:\OS\Net\lwip\source\core\pbuf.c

is it a bug???
i change code to:
        if(mem!=NULL)
                pbuf_free((struct pbuf *)mem);