public function get_associated_posts( $post_type = null ) {

		// If we're querying only posts, we can skip these associations entirely because courses don't support them.
		$post_types = 'course' !== $post_type ? get_post_types_by_support( 'llms-membership-restrictions' ) : array();

		// If we're looking at a single post type we only have to query associations for that post type.
		$post_types = $post_type ? array_intersect( $post_types, array( $post_type ) ) : $post_types;

		// Our return array.
		$posts = array();

		// Retrieve all posts that are restricted to a membership via a LifterLMS Membership Restriction setting.
		foreach ( $post_types as $type ) {
			$posts[ $type ] = $this->query_associated_posts( $type, '_llms_is_restricted', 'yes', '_llms_restricted_levels' );
		}

		// Include courses if courses were requested or if no specific post type was requested.
		if ( ! $post_type || 'course' === $post_type ) {
			$posts['course'] = $this->query_associated_courses();
		}

		/**
		 * Filter the list of posts associated with the membership.
		 *
		 * @since 3.38.1
		 *
		 * @param array[]         $posts     An array of arrays of post IDs. The array keys are the post type and the array values are arrays of integers.
		 * @param string|null     $post_type The requested post type if only a specific post type was requested, otherwise `null` to indicate all associated post types.
		 * @param LLMS_Membership $this      Membership object.
		 */
		$posts = apply_filters( 'llms_membership_get_associated_posts', $posts, $post_type, $this );

		// If a single post type was requested, return only that.
		if ( $post_type ) {
			// Return the request post type array and fallback to an empty array if that post type doesn't exist.
			return isset( $posts[ $post_type ] ) ? $posts[ $post_type ] : array();
		}

		// Remove empty arrays and return the rest.
		return array_filter( $posts );

	}