change error handling

Author: adityamittal13

fastchat/serve/monitor/monitor.py

@@ -1034,21 +1034,21 @@ def build_leaderboard_tab(
                 build_full_leaderboard_tab(
                     elo_results_text, model_table_df, model_to_score
                 )
-            try:
-                from fastchat.serve.monitor.copilot_arena import (
-                    build_copilot_arena_tab,
-                    copilot_arena_leaderboard_url,
-                )
 
-                if not copilot_arena_leaderboard_url:
-                    raise ValueError(
-                        "COPILOT_ARENA_LEADERBOARD_URL environment variable is not set. "
-                        "Please configure it to a valid URL."
-                    )
+            from fastchat.serve.monitor.copilot_arena import (
+                build_copilot_arena_tab,
+                copilot_arena_leaderboard_url,
+            )
+
+            if copilot_arena_leaderboard_url:
                 with gr.Tab("Copilot Arena Leaderboard", id=5):
                     build_copilot_arena_tab()
-            except Exception as e:
-                print(f"Unable to build Copilot Arena's Leaderboard. Error: {e}")
+            else:
+                print(
+                    "Unable to build Copilot Arena's Leaderboard. "
+                    "COPILOT_ARENA_LEADERBOARD_URL environment variable is not set. "
+                    "Please configure it to a valid URL."
+                )
 
         if not show_plot:
             gr.Markdown(