fix: TypeScript null check for originalUserId

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/mining-admin-service/src/application/services/users.service.ts

@@ -587,7 +587,9 @@ export class UsersService {
       });
 
       const userIdToSeq = new Map(
-        ancestorReferrals.map((r) => [r.originalUserId.toString(), r.accountSequence]),
+        ancestorReferrals
+          .filter((r) => r.originalUserId !== null)
+          .map((r) => [r.originalUserId!.toString(), r.accountSequence]),
       );
 
       // 按顺序获取每个祖先的详细信息