Just wanted to post a possible "simple" solution to a PA bug/annoyance that has been plaguing users for years based on this forum. It took me months of searching and trying everything to find a solution that works for my own flows.
Issue: The expression "null" in update sharepoint item does not actually work for some fields (especially single choice columns, but even multi choice if not done properly). I have seen some solutions using the HTTP request feature but have not used this myself and did not want to complicate my flows.
Solution:
- null expression for fields where it works (date, string seem to be ok)
- for multi choice fields select "switch to input entire array" on the right side of the field (looks like a little square with a T inside 
) first and then use the null expression
- for single choice fields, what worked for me was to create a string variable at the start of the flow with an empty initial value and then I assigned this variable to all the single choice fields that wouldn't clear with the null expression (in the flow it will appear that you are assigning a custom value with the big blue X but checking the list item after running this flow, the choice field has been correct set to no choice)
Hope that also works for others and helps someone!
