The method getException() does not exist on Elgg\Http\ResponseBuilder. Since it exists in all sub-types, consider adding an abstract or default implementation to Elgg\Http\ResponseBuilder.
Ignorable by Annotation
If this is a false-positive, you can also ignore this issue in your code via the ignore-call annotation
The expression return $this->send($this...or_page, $status_code)) could also return false which is incompatible with the documented return type Symfony\Component\HttpFoundation\Response. Did you maybe forget to handle an error condition?
If the returned type also contains false, it is an indicator that maybe an error condition leading to the specific return statement remains unhandled.