#3355729 Trying to save any theme settings form results in WSoD

src/Form/DevelFormHelperTrait.php

src/Form/EmbeddedEnforceForm.php

src/Form/ThemeSettingsFormTrait.php

src/FormHandler/DevelEnforceFormHandler.php

src/FormHandler/ThemeSettingsFormHandlerTrait.php

tests/src/Functional/ThemeSettingsFormTest.php