No cache for NS RR in public DNS

[Tech W.]

Hello,

like this domain:

blogchina.org

I can't get its NS RR in public DNS:

dig blogchina.org ns @8.8.8.8

get nothing.

But it does work correctly.
for example, query the record:

dig udb.yy.blogchina.org

works!

How to setup Bind for this?

Thanks!