class DateInterval is not a primitive type

Ran into this problem during a project. Where we use the JSON API to unlock Drupal fields to a decoupled front end.

After installing the patch we get values back and the error message regarding sterilization is gone.

Our error message:
TypeError: Drupal\serialization\Normalizer\PrimitiveDataNormalizer::normalize(): Return value must be of type ArrayObject|array|string|int|float|bool|null, DateInterval returned in Drupal\serialization\Normalizer\PrimitiveDataNormalizer->normalize()

Same problem here, With drupal 9.5 and the JSONAPI we had no problem (but the duration field was null).
with drupal D10.1.5 we ran into the same prvious error message in the JSONAPI.
And the patch fixed the error and also now the duration field is not null

                "field_duration": {
                    "seconds": 3600,
                    "duration": "PT1H"
                },

After upgrading to D10, we had the same issue and error with JSONAPI endpoints that contained Duration fields. Endpoints with Duration fields were unavailable and this error displayed in the error logs when trying to access them:
TypeError: Drupal\serialization\Normalizer\PrimitiveDataNormalizer::normalize(): Return value must be of type ArrayObject|array|string|int|float|bool|null, DateInterval returned in Drupal\serialization\Normalizer\PrimitiveDataNormalizer->normalize() (line 36 of /var/www/html/web/core/modules/serialization/src/Normalizer/PrimitiveDataNormalizer.php).

Just confirming that the patch resolved the issue for us.

Same here, the patch #7 resolved the issue for me.
I'm on a Drupal 10.1.6

Fixed minor issues with #7 patch and added Unit Test for normalizer

Automatically closed - issue fixed for 2 weeks with no activity.