ntabs
5
In your action, you must’ve added the field with an empty value. Only make changes to a field that you’re changing
I’m positive this is how your action looks like:
Make changes to thing action
field 1 = new value
field 2 = new value
field 3 = empty
field 4 = new value
if you’re only changing the values for field 1, 2, and 4, you must not add field 3.
If you want to change multiple fields in one action, you can add a default data source of the inputs referencing to its value and on your action simply reference to all the corresponding inputs 
Let me know if this helps