There is a comma between each line so if there are multiple extensions there is alway a line with just a comma in between. Like that
example
,
filter configuration
,
placeholders
Sorry for not claryfying this earlier, I just noticed this too. This structure is constant. It would not be a problem for me, though, removing these commas so equaling the N from "[N]" with the line number from the field "message_extension" is possible.