Got undefined variable error

Got undefined variable $b errors at line 1272 of /includes/calendar/class-calender_generator.php file. I added an “isset” to fix the error.
$evcal_terms = (isset($b) && $b==1)? $ett_terms: wp_get_post_terms($event_id,$__tax_slug);

Don’t know when it started happening. Please fix.

The plugin version is 2.4.