From fd6f3ed2bc8f83428cdd5e31ef8313e9af862b07 Mon Sep 17 00:00:00 2001
From: Yang Xu <xuyang@me.com>
Date: Fri, 12 Aug 2022 14:59:17 +0800
Subject: [PATCH] fix a bug of delete transaction

---
 Sources/PersistentHistoryTrackingKit/Cleaner.swift | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/Sources/PersistentHistoryTrackingKit/Cleaner.swift b/Sources/PersistentHistoryTrackingKit/Cleaner.swift
index 99bef41..dc4cfca 100644
--- a/Sources/PersistentHistoryTrackingKit/Cleaner.swift
+++ b/Sources/PersistentHistoryTrackingKit/Cleaner.swift
@@ -29,19 +29,23 @@ struct Cleaner: TransactionCleanerProtocol {
     func cleanTransaction(before timestamp: Date?) throws {
         guard let timestamp = timestamp else { return }
         try backgroundContext.performAndWait {
-            let request = getPersistentStoreRequest(before: timestamp, for: authors)
-            try backgroundContext.execute(request)
+            if let request = getPersistentStoreRequest(before: timestamp, for: authors) {
+                try backgroundContext.execute(request)
+            }
         }
     }
 
     // make a request for delete transactions before timestamp
-    func getPersistentStoreRequest(before timestamp: Date, for allAuthors: [String]) -> NSPersistentStoreRequest {
+    func getPersistentStoreRequest(before timestamp: Date, for allAuthors: [String]) -> NSPersistentStoreRequest? {
         let historyStoreRequest = NSPersistentHistoryChangeRequest.deleteHistory(before: timestamp)
         if let fetchRequest = NSPersistentHistoryTransaction.fetchRequest {
             fetchRequest.predicate = createPredicateForAllAuthors(allAuthors: authors)
             historyStoreRequest.fetchRequest = fetchRequest
+            return historyStoreRequest
+        }
+        else {
+            return nil
         }
-        return historyStoreRequest
     }
 
     /// create predicate for all authors