Custom WebformComposite element throws DumpException

Creating a new Webform element based on WebformCompositeBase results in a DumpException being thrown.

Uncaught PHP Exception Symfony\\Component\\Yaml\\Exception\\DumpException: "Object support when dumping a YAML file has been disabled." at /var/www/html/vendor/symfony/yaml/Inline.php line 197

I traced the issue back to modules/contrib/webform/src/Plugin/WebformElementBase.php

The getDefaultMultipleProperties() function is returning translatable objects instead of strings for some properties (multiple__add_more_button_label for example).

To work around this issue, I implemented the function in my plugin class, and casted to string.