Warning error after updating

Following on this thread;

link

I'm noticing all the v2 Perch websites have the message;

Warning: count(): Parameter must be an array or an object that implements Countable in /home/XXXXXXXXXX/public_html/perch/core/lib/PerchFieldTypes.class.php on line 69

I've recently updated our server to php7.2 and for all v2 sites I updated them to 2.8.34. The fix to upgrade the site in the other thread to V3 was OK as it was a simple site, but I currently have about 30 v2 sites and I've generally only updating to v3 when they've required working on. Is upgrading to v3 the only way to get round this error? The front-end of the sites are OK its just in the admin I get this message.