fix: close analytics review findings

backend/src/routes/analytics.ts

@@ -64,7 +64,7 @@ router.get(
       from: from as string,
       to: to as string,
       accountId: accountId ? Number(accountId) : undefined,
-      categoryId: categoryId ? Number(categoryId) : undefined,
+      categoryId: categoryId !== undefined ? Number(categoryId) : undefined,
       onlyConfirmed: onlyConfirmed === 'true',
       granularity: granularity as Granularity,
     });