Getting a non fatal error

Pretty minor one, its only a warning but it would be great if it could be fixed?

Non fatal error triggered on: https://boomersclub.com.au/xmlrpc.php Array
(
[type] => 8192
[message] => stripslashes(): Passing null to parameter #1 ($string) of type string is deprecated
[file] => /****/plugins/decimal-product-quantity-for-woocommerce/includes/functions.php
[line] => 960