fix: balance contract braces and resolve undefined string assignment in batch validation

Author: N-thnI

contract/contracts/hello-world/src/lib.rs

@@ -392,6 +392,8 @@ impl AutoShareContract {
     /// Emits a `BatchProcessingCompleted` event for off-chain listeners.
     pub fn emit_batch_completed(env: Env, batch_id: BytesN<32>, processed_count: u32) {
         autoshare_logic::emit_batch_completed(env, batch_id, processed_count).unwrap();
+    }
+
     // ============================================================================
     // Batch Notification Creation
     // ============================================================================

listener/src/services/batch-validation-service.ts

@@ -187,7 +187,7 @@ export class BatchValidationService {
       } else {
         invalidEntries.push({
           index,
-          error: validation.error,
+          error: validation.error ?? '',
         });
       }
     });