These changes are covered by unit tests. But you can also manually confirm it is working if you wish, for Moodle 2.7. Follow the instructions in the description and then after applying this patch press 'Recalculate Now' button that appears on the main page of the Statistics report. Click on the hyperlink 'Variant 9 of calculated 1' to see the response analysis for variant 9 of the question 'calculated 1'. Look at the table titled 'Analysis of responses'. Now there is a '1' in the count for the ' [Did not match any answer] ' row and other rows have a zero count. Also there is a column in the table 'Actual response' with a '0' in the ' [Did not match any answer] ' row and nothing in other rows.