Sami I

Results 2 issues of Sami I

Description of changes: Adding missing attribution to the ndistinct README By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

if a user enables ```enable_hint_table``` and ```enable_hint``` but the ```hint_plan.hints``` does not exist, it will lead to query failure. I don't think this should result in an error, but should...