This is an issue identified from the PCS testsuite when using MW REST API instead of parsoid on restbase.
When we send an API request to /v1/page/{title} for non-html content, the response is a 500 error.
For the same page/html request for parsoid on restbase, the response is the page rendered as HTML.

Steps to reproduce:

• For the page: Schema:RelatedArticles
• Parsoid page/html output on restbase returns an HTML rendered version of the JSON:
  • https://meta.wikimedia.org/api/rest_v1/page/html/Schema%3ARelatedArticles
• MW REST API output of parsoid raises an error:
  • https://meta.wikimedia.org/w/rest.php/v1/page/Schema%3ARelatedArticles/html