up

app/src/main/java/io/legado/app/help/storage/Backup.kt

@@ -45,28 +45,44 @@ object Backup {
     }
 
     private fun backupBookshelf(path: String) {
-        val json = GSON.toJson(App.db.bookDao().allBooks)
+        App.db.bookDao().allBooks.let {
+            if (it.isNotEmpty()) {
+                val json = GSON.toJson(it)
                 val file = FileHelp.getFile(path + File.separator + "bookshelf.json")
                 file.writeText(json)
             }
+        }
+    }
 
     private fun backupBookSource(path: String) {
-        val json = GSON.toJson(App.db.bookSourceDao().all)
+        App.db.bookSourceDao().all.let {
+            if (it.isNotEmpty()) {
+                val json = GSON.toJson(it)
                 val file = FileHelp.getFile(path + File.separator + "bookSource.json")
                 file.writeText(json)
             }
+        }
+    }
 
     private fun backupRssSource(path: String) {
-        val json = GSON.toJson(App.db.rssSourceDao().all)
+        App.db.rssSourceDao().all.let {
+            if (it.isNotEmpty()) {
+                val json = GSON.toJson(it)
                 val file = FileHelp.getFile(path + File.separator + "rssSource.json")
                 file.writeText(json)
             }
+        }
+    }
 
     private fun backupReplaceRule(path: String) {
-        val json = GSON.toJson(App.db.replaceRuleDao().all)
+        App.db.replaceRuleDao().all.let {
+            if (it.isNotEmpty()) {
+                val json = GSON.toJson(it)
                 val file = FileHelp.getFile(path + File.separator + "replaceRule.json")
                 file.writeText(json)
             }
+        }
+    }
 
     private fun backupPreference(path: String) {
         Preferences.getSharedPreferences(App.INSTANCE, path, "config")?.let { sp ->