Form with only file upload fails `populateFromPostAndValidate()`

Controller

	public function function(Form $form, Model $model, FormHydrator $formHydrator, ServerRequestInterface $request): ResponseInterface
	{
		$uploadedFiles = $request->getUploadedFiles();
		if (isset($uploadedFiles['Form']['sourceImage'])) {
			$form->sourceImage = $uploadedFiles['Form']['sourceImage'];
		}

		if ($formHydrator->populateFromPostAndValidate($form, $request)) {
			$model->dostuff($form); // never reached
		}

		return $this->viewRenderer->render('page', ['form' => $form, 'model' => $model]);
	}

Form

<?php

declare(strict_types=1);

namespace App\Form;

use Psr\Http\Message\UploadedFileInterface;
use Yiisoft\Validator\LabelsProviderInterface;
use Yiisoft\Validator\Rule\Image\Image;
use Yiisoft\Validator\Rule\Required;
use Yiisoft\Validator\RulesProviderInterface;

class Form extends \Yiisoft\FormModel\FormModel implements LabelsProviderInterface, RulesProviderInterface
{
	public ?UploadedFileInterface $sourceImage = null;

	public function getPropertyLabels(): array
	{
		return [
			'sourceImage' => _('Source Image'),
		];
	}

	public function getValidationPropertyLabels(): array
	{
		return $this->getPropertyLabels();
	}

	public function getRules(): array
	{
		return [
			'sourceImage' => [new Required(), new Image(minWidth: 80, skipOnEmpty: true)],
		];
	}
}

With only 1 (or more?) field, that field being a file upload, populateFromPostAndValidate() never returns true. I suspect this is caused by $request->getParsedBody() being empty under such circumstances.

Start at FormHydrator::populateFromPostAndValidate() and inspect how it handles an empty $request->getParsedBody() when uploaded files are present. Reproduce the controller example with the Form model and its sourceImage rules, then verify that validation succeeds for a form containing only the file upload.