Assign:Object reference not set to an instance of an object. Calculate Client Security Hash

Good morning everyone, Today still continue my activities in UiPath Academy, and now I do the exercise called Calculate Client Security Hash in the Level 3 - Advanced Training, all was good until in a one part of the execution, the exercise show this error:

In this part of sequence:


If someone know a explanation when this error appear, or in other occasion someone of you, have the opportunity to fix error, explain me because I want to know a explanation.
For other hand, I don’t know but I try to change the type of the variable of TransactionData to DataRow but also It’s doesn’t work, but the message error say that some reference is not instance in a some object, also I think that the variable WILIST have DataRow type, but I’m confused.
Sorry, and Thank you.

Your list is probably null when you’re trying to set it. Set the default value of WIList to New List(Of String), and it should work.

Thank you @Anthony_Humphries but WIList is DataRow, If I declare this variable as you said, the variable show an error about the type of variable.

Check where you’re loading data into this datarow. I suspect that you have a null datatable or a null reference being passed to the table.

I have this part in GetTransactionData:

In other in the Extract_WorkItems:

I’m sorry, because I don’t know where is located.

Check your Init state and make sure the initial data is being prepared properly. Then, use Step Into and Step Over in debug mode while monitoring the status of your transaction items and transaction table. That way, you’ll see if data is being inserted into your table for reading.


It means that TransactionData is having a null value. You might not pass it correctly from the arguments/activity to get the value.

Please check your workflow again.

Thank you @Anthony_Humphries @khairuln guys, thank you for all, both is was in the correct. The problem was the next:

I don’t know why but in a some moment I am deleted the value of me argument, and all of two say correct answer, thank you.


That’s great you found the cause. Make sure to pass it again and we can move on with our lunch now.


UiPath is a little finicky when it comes to arguments. If you change the name or datatype of an argument in a workflow, you have to re-enter the argument again every time you invoke the workflow.

ohh this the reason why, I see the argument withe their value, and after I was think hey I remember that I put this value. Thank you sir

Thank you, well I was can’t lunch for something situation, but normal I eating a dessert for more energy :rofl:

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Hi All,

I have tried all the possible solutions but nothing to be working. Would be great if someone could please help. I am trying to upload my project zip file but unable to.

Thanks much