fatal error on config inspector

Problem/Motivation

When we use config inspector this fatal is triggerred

Symfony\Component\Validator\Exception\UnexpectedTypeException: Expected argument of type "array", "string" given in Drupal\Core\Validation\Plugin\Validation\Constraint\ValidKeysConstraintValidator->validate() (line 33 of core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/ValidKeysConstraintValidator.php).

Steps to reproduce

Install the module
attach library
export config
install config inspector
go on config inspector page