Avoid NULL deref is the there's no request body yet
@@ -1392,7 +1392,7 @@ void tunnel_write(struct st_h2o_http3_server_stream_t *stream)
assert(!stream->tunnel->up.is_inflight);
- if ((bytes_to_send = stream->req_body->size) == 0)
+ if (stream->req_body == NULL || (bytes_to_send = stream->req_body->size) == 0)
return;
/* move chunk of data into stream->tunnel.up.buf */
