Hi all: In example6_app(void),void newdata(void){ struct example6_state *s = (struct example6_state *)uip_conn->appstate; if(s->state == STATE_WAITING) { s->state = STATE_HELLO; s->dataptr = "hello "; s->datalen = 6; }When s->datalen = 6,it runs well,But if i chang s->datalen = 0,it does't run wellwhy?