fix: handle empty markdown

src/helpers/markdown.ts

@@ -7,6 +7,7 @@ export function readDuration(markdown: string): number | undefined {
 }
 
 export function markdownToHtml(markdown: string): string {
+  if (!markdown) return "";
   const md = new MarkdownIt({
     html: false, // set to true only if you trust the source
     linkify: true,