breakoutSets bug within the `get_survey_responses` method

Good afternoon,

I added a pull request, and will reference it.  But there was a missing comma in the `valid_keys` list.  The raise statement was also confusing for me, give what was told as valid wasn't showing this as an option despite it being an option.

The pull request makes the assert and raise consistent with the list, and the list is fixed to include the missing comma.