Python activity odd error

Every now and again (running 100’s of flows). I am getting an odd error with the python activity:

strong textSystem.ArgumentNullException: String reference not set to an instance of a String.
strong textParameter name: s

I thought it might be an issue with what I am sending back so I just dropped a file from python and I am no longer sending anything back to uipath and I still randomly get this message on a flow or 2. I have checked the code and recreated the situation but 9 out of 10 times it works. Also, I am passing nothing back now so it can’t be that (and the python finishes as dropping the file in a shared drive is the last thing it does). I am starting to think this may be a bug. Though if anyone else has any ideas I am willing to try them.


Welcome to forums

As you are seeing in the error it’s a Argument Null Exception

It’s because if you are passing any null value to arguments then this type of exception will happen

So when you are getting this error, make a check on the arguments you are passing

Hope this may help you


Hi srini84 as noted its not null and nothing is being passed back (I use an activity now to just pull i the file. Also, please note it will run 9 out of 10 times fine and randomly fail 1 time (python completes 10 out of 10 times). The python is 100% successful (I have a file I can see with the values that should be in them). So I have no clue where this null value is coming from.


Can you share the entire error you are getting?


System.InvalidOperationException: Python deserialization exception —> System.ArgumentNullException: String reference not set to an instance of a String.
Parameter name: s
at System.Text.Encoding.GetBytes(String s)
at UiPath.Shared.Service.PythonResponse.Deserialize(String json)
— End of inner exception stack trace —
at UiPath.Shared.Service.PythonResponse.Deserialize(String json)
at UiPath.Python.Service.PythonProxy.RequestAsync(PythonRequest request, CancellationToken ct)
at UiPath.Python.Service.PythonProxy.Shutdown()
at UiPath.Python.Impl.OutOfProcessEngine.Release()
at UiPath.Python.Activities.PythonScope.Cleanup()
at UiPath.Python.Activities.PythonScope.OnCompleted(NativeActivityContext context, ActivityInstance completedInstance)
at System.Activities.Runtime.ActivityCompletionCallbackWrapper.Invoke(NativeActivityContext context, ActivityInstance completedInstance)
at System.Activities.Runtime.CompletionCallbackWrapper.CompletionWorkItem.Execute(ActivityExecutor executor, BookmarkManager bookmarkManager)