TypeError: preg_match(): Argument #2 ($subject) must be of type string, int given with 6.1.0

[Universal-Omega]

TypeError: preg_match(): Argument #2 ($subject) must be of type string, int given
vendor/justinrainbow/json-schema/src/JsonSchema/Constraints/ObjectConstraint.php:69

This did not happen before 6.1.0.

There is no indication of what (if anything) is actually causing it in our schema etc...

• The schema we use