public function __clone() {
		$this->maybe_read_meta_data();
		if ( ! empty( $this->meta_data ) ) {
			foreach ( $this->meta_data as $array_key => $meta ) {
				$this->meta_data[ $array_key ] = clone $meta;
				if ( ! empty( $meta->id ) ) {
					$this->meta_data[ $array_key ]->id = null;
				}
			}
		}
	}