made all members of EncryptionResult nullable

lib/models/encryption_result.dart

@@ -1,15 +1,15 @@
 import 'dart:typed_data';
 
 class EncryptionResult {
-  final Uint8List encryptedData;
-  final Uint8List key;
-  final Uint8List header;
-  final Uint8List nonce;
+  final Uint8List? encryptedData;
+  final Uint8List? key;
+  final Uint8List? header;
+  final Uint8List? nonce;
 
   EncryptionResult({
-    required this.encryptedData,
-    required this.key,
-    required this.header,
-    required this.nonce,
+    this.encryptedData,
+    this.key,
+    this.header,
+    this.nonce,
   });
 }