CustomElementsJsonResponse::setData() return type is not PHP7 compatible

This belongs into lupus_ce_renderer issue queue, which has its own d10 compatible version. Please make sure you are using the most recent one and provide more information then.

Updated issue description to better describe Drupal 9 / 10 differences regarding method return types.

Understood. Given https://www.drupal.org/node/3295154 → I don'T think this very critical but valid. MR welcome!

this is about php7 compatibility. I don't think we need to care about this any more, d9 is not a support release any more. We could instead add an issue to mark d9 as unsupported.