not failing on missing 'categories' in .md file's

frontmatter header

classes.py

@@ -4,6 +4,7 @@ import shutil
 from collections import defaultdict
 import markdown
 import frontmatter
+from bs4 import BeautifulSoup
 from pathlib import Path
 from logger import logger
 from config import Config
@@ -114,7 +115,7 @@ class Site:
 
     def map_categories(self):
         for content_item in self.content_items:
-            for category in content_item.data.get("categories"):
+            for category in content_item.categories:
                 if not category == "default":
                     self.categories[category].append(content_item.slug)