Yasuki Okumura

Results 2 issues of Yasuki Okumura

**Public API Changes** None **Description** The tfclient had a problem to unsubscribe in the callback because `splice` doesn't work well in the iterating. This PR fixed the problem to copy...

Without this validation, "panic: runtime error: slice bounds out of range" may happen. I added validation which ensure length should not be less than 1.