fix: handle empty markdown

src/helpers/markdown.ts

@@ -2,6 +2,7 @@ import MarkdownIt from "markdown-it";
 const parser = new MarkdownIt();
 
 export function readDuration(markdown: string): number | undefined {
+  if (!markdown) return;
   const words = markdown.split(" ")?.filter(Boolean)?.length;
   return words && Math.round(words / 250);
 }