ListFieldEnhancer do not work

Problem/Motivation

Using the ListFieldEnhancer for a list field (text) does not work.

Error message:
TypeError: Adaptor Drupal\jsonapi_extras\Plugin\ResourceFieldEnhancerBase returned invalid output data: [] in Drupal\jsonapi_extras\Plugin\ResourceFieldEnhancerBase->undoTransform() (Zeile 66 in /var/www/html/vendor/e0ipso/shaper/src/DataAdaptor/DataAdaptorTransformerTrait.php).

I tried to debug it but I don't understand what is wrong with $data value (see screenshot).

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes