With give-form-field-manager 2.1.0:
PHP Fatal error: Uncaught TypeError: Return value of GiveFormFieldManager\FormFields\ValueObjects\FieldType::getFieldsApiType() must be of the type string, null returned in […]/wp-content/plugins/give-form-field-manager/src/FormFields/ValueObjects/FieldType.php:73
getFieldsApiType is declared to return a string and then the action_hook option returns an explicit null. Changing “null” to “”” (empty string) at least keeps it from exploding.