PHP warning in Runway (S3 Backup) for PHP 7.2

I'm not sure if this is something specific to my hosting setup or applies to all setups. My S3 backup is working fine, but I've seen the message below is being logged in error_log - every day at the time of the daily backup.

The same message is appearing daily in 4 sites running Runway in PHP 7.2. I don't see the message in another Runway site that's running PHP 7.1, so maybe its a coding issue in the CurlFactory.php file in Runway that's specific to PHP 7.2?

[20-Dec-2018 11:30:02 UTC] PHP Warning:  count(): Parameter must be an array or an object that implements Countable in /home/xxxxxxxx/public_html/perch/core/runway/apps/perch_s3/lib/guzzlehttp/guzzle/src/Handler/CurlFactory.php on line 67