public function fixIsbnNumber( $isbn_number ) {

		// Regex to split a string only by the last whitespace character
		@list( $isbn_number, $addon ) = preg_split( '/\s+(?=\S*+$)/', trim( $isbn_number ) ); // @codingStandardsIgnoreLine

		$isbn_number = ( new \Isbn\Isbn() )->hyphens->fixHyphens( $isbn_number );

		if ( $addon ) {
			$isbn_number .= " $addon";
		}

		return $isbn_number;
	}