Bug fix on messages with timestamp being '0'

Whatsapp_Chat_Exporter/data_model.py

@@ -27,7 +27,7 @@ class Timing:
         Returns:
             Optional[str]: Formatted timestamp string, or None if timestamp is None
         """
-        if timestamp:
+        if timestamp is not None:
             timestamp = timestamp / 1000 if timestamp > 9999999999 else timestamp
             return datetime.fromtimestamp(timestamp, TimeZone(self.timezone_offset)).strftime(format)
         return None