fix(trajectory): fix division by zero and None handling in name normalization

explorer.py

@@ -1653,7 +1653,7 @@ def build_trajectories_tab(db_path: str, window_size: str) -> None:
     def normalize_mp_name(name):
         """Normalize MP name for better matching between data sources."""
         if not name:
-            return name
+            return ""
         # Remove extra whitespace
         name = name.strip()
         # Ensure consistent spacing after comma
@@ -1678,9 +1678,12 @@ def build_trajectories_tab(db_path: str, window_size: str) -> None:
         all_mp_names.update(positions.keys())
 
     matched_names = sum(1 for mp in all_mp_names if mp in party_map)
+    if all_mp_names:
         logger.info(
             f"MP name matching: {matched_names}/{len(all_mp_names)} matched ({100 * matched_names / len(all_mp_names):.1f}%)"
         )
+    else:
+        logger.info("MP name matching: no MPs found in positions data")
 
     if matched_names == 0 and len(all_mp_names) > 0:
         logger.warning("No MP names matched between positions and party_map!")