correct assertions

packages/website/src/pages/[...chunk_default]/[...locale]/session/_index.tsx

@@ -91,15 +91,17 @@ function Content() {
         ? deltaTankStats(session.player.stats, tankStatsB)
             .sort((a, b) => b.last_battle_time - a.last_battle_time)
             .flatMap((entry) => {
+              if (!(entry.tank_id in tankDefinitions.tanks)) return [];
+
               const tank = tankDefinitions.tanks[entry.tank_id];
-              if (!tank) return [];
+
+              if (!(tank.id in averageDefinitions.averages)) return [];
 
               const average = averageDefinitions.averages[tank.id];
-              if (!average?.mu) return [];
 
               const composite = compositeStats(
                 { ...entry.all, battle_life_time: entry.battle_life_time },
-                average.mu,
+                average.mu!,
               );
 
               return [{ tank, composite }];