add type assertion checked
add type assertion checked

License: MIT
Signed-off-by: Kejie Zhang <ef73032e2230a54f9c6e6f2afb55d429e3c41ed0@qq.com>

Luzifer/go-ipfs,chriscool/go-ipfs,chriscool/go-ipfs,Luzifer/go-ipfs,Luzifer/go-ipfs,chriscool/go-ipfs