Tracked it down to r44015 (Article.php):

...
+ function replaceSection( $section, $text, $summary = '', $edittime = NULL ) {

		wfProfileIn( __METHOD__ );

• if( $section == '' ) {
• // Whole-page edit; let the text through unmolested.

+ if( $section === '' ) {
+ // Whole-page edit; let the whole text through
...

If you edit through the API, $section is null here, so the identity operator won't work here.

I'd suggest to just use ..if(!$section) .. or would that be bad style?

On second thought, (!$section) of course wouldn't work, as '0' is false, too. So probably just change it back to ($section == '').

I'm marking this bug as blocker for now, as it really should be fixed before the next scap, or else the bots out there would create a giant mess on all projects within minutes.

(In reply to comment #2)

On second thought, (!$section) of course wouldn't work, as '0' is false, too.
So probably just change it back to ($section == '').

I'm marking this bug as blocker for now, as it really should be fixed before
the next scap, or else the bots out there would create a giant mess on all
projects within minutes.

Good idea. I'll tell Brion about this to make sure he doesn't accidentally scap this. I'd fix it earlier, but I'm kind of busy this week and I haven't looked into the possible side effects of changing === '' back to == ''.

(In reply to comment #3)

and I haven't looked
into the possible side effects of changing === '' back to == ''.

Turns out I didn't need to, passing '' instead of null was good enough. Fixed in r44394.