Fix RSS feed not handling None values (#569)

Previously, the 'sanitize' function would throw an error when 'text' was None. This commit fixes the issue by adding a check to handle the case where 'text' is None, returning an empty string instead.

Closes #568

bookmarks/feeds.py

@@ -16,6 +16,8 @@ class FeedContext:
 
 
 def sanitize(text: str):
+    if not text:
+        return ''
     # remove control characters
     valid_chars = ['\n', '\r', '\t']
     return ''.join(ch for ch in text if ch in valid_chars or unicodedata.category(ch)[0] != 'C')