The CreateHandler::beforeExecute() method can be simplified by returning void instead of it's arguments

This can be simplified to:

/**
 * @param \Magento\Catalog\Model\Product\Gallery\CreateHandler $mediaGalleryCreateHandler
 * @param string $entityType
 * @param \Magento\Catalog\Model\Product $product
 * @return void
 */
public function beforeExecute(
	\Magento\Catalog\Model\Product\Gallery\CreateHandler $mediaGalleryCreateHandler,
	$entityType,
	\Magento\Catalog\Model\Product $product
) {
	$attribute = $mediaGalleryCreateHandler->getAttribute();
	$mediaCollection = $this->getMediaEntriesDataCollection($product, $attribute);
	if (!empty($mediaCollection)) {
		$storeDataCollection = $this->loadStoreViewVideoData($mediaCollection, $product->getStoreId());
		$mediaCollection = $this->addAdditionalStoreData($mediaCollection, $storeDataCollection);
		$product->setData(
			$attribute->getAttributeCode(),
			$mediaCollection + $product->getData($attribute->getAttributeCode())
		);
	}
}

A trick: a Ā«beforeĀ» plugin can return nothing if it needs not modify any argument