use option argument

packages/presentation/src/client/services/renderer/extract-sections.ts

@@ -5,7 +5,7 @@ import { findAfter } from 'unist-util-find-after';
 import { visit } from 'unist-util-visit';
 
 
-function wrapWithSection(parentNode: Parent, startElem: Node, endElem: Node | undefined | null, isDarkMode?: boolean): void {
+function wrapWithSection(parentNode: Parent, startElem: Node, endElem?: Node | null, isDarkMode?: boolean): void {
   const siblings = parentNode.children;
 
   const startIndex = siblings.indexOf(startElem);

packages/remark-drawio/src/services/renderer/remark-drawio.ts

@@ -21,7 +21,7 @@ declare module 'mdast' {
 
 type Lang = 'drawio';
 
-function isDrawioBlock(lang: string | undefined | null): lang is Lang {
+function isDrawioBlock(lang?: string | null): lang is Lang {
   return /^drawio$/.test(lang ?? '');
 }