NCBC-499: Refactor InternalPoolImpl so that NRE is not thrown

Change-Id: Ie4a757a320b988446ab0e5a63db314c67dc3818f
Reviewed-on: http://review.couchbase.org/37840
Reviewed-by: Jeffry Morris <jeffrymorris@gmail.com>
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>