Update app.py

app.py

@@ -146,6 +146,8 @@ def generate_session_token() -> str:
 
 def sanitize_input(text: str) -> str:
     """Sanitize user input to prevent XSS and injection attacks."""
+    if not text:
+        return ""
     return bleach.clean(text.strip(), tags=[], attributes={}, protocols=[], strip=True)
 
 def validate_name(name: str) -> str: