[BUG] Using Error Handler in Custom Extension

[timdreier]

Describe the bug
I want to throw a 410 (404) error inside my Controller. However, I only get a blank Page using the error handler.

To Reproduce
Steps to reproduce the behavior:

Call the ErrorHandler in Controller:

$message = 'The page you requested is no longer available.';

$errorHandler = $this->getErrorHandlerFromSite($GLOBALS['TYPO3_REQUEST'], 410);
if ($errorHandler instanceof PageErrorHandlerInterface) {
    $response = $errorHandler->handlePageError($GLOBALS['TYPO3_REQUEST'], $message);
} else {
    $response = $this->handleDefaultError($GLOBALS['TYPO3_REQUEST'], 410, $message);
}

return $this->throwStatus(410, $message, $response->getBody()->getContents());

Expected behavior
Error page shows

Additional context
Interesting: (string) $response->getBody() returns the HTML of the current Page and the Error Page. $response->getBody()->getContents() is a empty string.