code: protected function isExpectingContent($request): bool
      {
          $methods = $this->route->isNotRelationship() ? ['POST', 'PATCH'] : ['POST', 'PATCH', 'DELETE'];
  
          return \in_array($request->getMethod(), $methods);
      }
docs: Is data expected for the supplied request?
  
  If the JSON API request is any of the following, a JSON API document
  is expected to be set on the request:
  
  - Create resource
  - Update resource
  - Replace resource relationship
  - Add to resource relationship
  - Remove from resource relationship
  
  @param Request $request
  @return bool