	protected function get_parent( $parent ) {
		$error = new WP_Error( 'rest_post_invalid_parent', __( 'Invalid post parent ID.' ), array( 'status' => 404 ) );
		if ( (int) $parent <= 0 ) {
			return $error;
		}

		$parent = get_post( (int) $parent );
		if ( empty( $parent ) || empty( $parent->ID ) || $this->parent_post_type !== $parent->post_type ) {
			return $error;
		}

		return $parent;
	}