Fix set null to empty in proto (#355)

Author: MaxHeimbrock

Runtime/Scripts/DataStreams/ByteDataStream.cs

@@ -112,8 +112,8 @@ public WriteToFileInstruction WriteToFile(string directory = null, string nameOv
             using var request = FFIBridge.Instance.NewRequest<ByteStreamReaderWriteToFileRequest>();
             var writeToFileReq = request.request;
             writeToFileReq.ReaderHandle = (ulong)_handle.DangerousGetHandle();
-            writeToFileReq.Directory = directory;
-            writeToFileReq.NameOverride = nameOverride;
+            if (directory != null) writeToFileReq.Directory = directory;
+            if (nameOverride != null) writeToFileReq.NameOverride = nameOverride;
 
             var instruction = new WriteToFileInstruction(request.RequestAsyncId);
             using var response = request.Send();