Headless Server: Deprecated content type 'application/graphql+json' not supported anymore

With the necessary update to Spring 7, the already deprecated usage of MediaType#APPLICATION_GRAPHQL was removed in Spring 7, thus can’t be used anymore. The recommended replacement is MediaType#APPLICATION_GRAPHQL_RESPONSE.

Follow Section, “Headless Server: Deprecated content type 'application/graphql+json' not supported anymore” for upgrade information.

(CMS-28677)