Could you share your revit file? Because your List.FirstItem node is already outputting “null”. 
Hi Danny,
As a appreciation of your hard work I’m willing to provide you award for exceeding the meaning of the word help. Could you provide your email please? Or you can send an e-mail titomoura@gmail.com.
Thank you.
At first view it seems that the script is not recognizing/ finding any stairs in your model.
Maybe you could try selecting the families you want to edit by hand instead of all elements in the category “stairs”. Then i would suggest using the “Select.Elements” node.
I am downloading the Revit file at the moment but my internet is quite slow
I see now, your stairs in the Revit file are not actually stairs, but generic models!
New result:
The dyn file:
31-01-2020 Set Parameter of generic models by Closest Grid Name.dyn (51.5 KB)
The idea is to create a grid location for every single item in the project.
Okay let me take a look 
But you have to keep in mind that this will get really heavy on your computer. Your Revit probably will not be able to handle all your objects at once. (and most likely crash)
I have created this solution, but to prevent crashing your revit, i would recommend to run this script per level. So just open a level, run the script whilst in that view and then repeat this for every level.
31-01-2020 Set Comment Parameter of Closest Grid for Every Object.dyn (40.8 KB)
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