In your first commit d1b/westpac-balance-scraper@d1b6bf4a6997bceb34fde0c78c3c80cf8ad78481 you used asserts in two locations, so I was simply preserving the convention you'd established. I know asserts are removed with optimisation, but equally these assertions are to detect programming errors in the script (as they do not deal in user input nor Westpac-provided responses). It therefore seems a valid use of assertions to me.