Fix: Avoid NRE on CloudflareR2Service.GetAllObjects when no file in bucket (#173)

Author: paul-fresquet

src/ByteSync.ServerCommon/Services/Storage/CloudflareR2Service.cs

@@ -92,9 +92,9 @@ private string GetServerFileName(SharedFileDefinition sharedFileDefinition, int
         };
 
         var response = await client.ListObjectsV2Async(request, cancellationToken);
-        return response.S3Objects
+        return response.S3Objects?
             .Select(o => new KeyValuePair<string, DateTimeOffset?>(o.Key, o.LastModified))
-            .ToList();
+            .ToList() ?? [];
     }
 
     public async Task DeleteObjectByKey(string key, CancellationToken cancellationToken)

tests/ByteSync.Client.Tests/Services/Communications/Transfers/FileUploadProcessorTests.cs

@@ -109,6 +109,8 @@ public async Task ProcessUpload_ShouldStartUploadWorkers()
             .Returns(Task.CompletedTask);
         _mockFilePartUploadAsserter.Setup(x => x.AssertUploadIsFinished(It.IsAny<SharedFileDefinition>(), It.IsAny<int>()))
             .Returns(Task.CompletedTask);
+        _mockFileUploadCoordinator.Setup(x => x.WaitForCompletionAsync())
+            .Returns(Task.Delay(150)); // Small delay to let tasks start
 
         // Act
         await _fileUploadProcessor.ProcessUpload(_sharedFileDefinition);