Clearing Lookup fields in SharePoint using Power Automate

A quirky one I came across recently that I figured I'd share!

I have a Power App that uses a SharePoint list, which in turn uses a field which is a lookup into a second SharePoint list.

I wanted to clear the values from the lookup field in SharePoint using Power Automate, i.e., removing any lookup value and leaving it empty.

Should be easy, right? Famous last words ... 😊

In Power Automate SharePoint lookup fields present like this in the Update Action:

Note the 'Id' at the end of the Field Name ... essentially SharePoint stores the lookup value as the List Item ID of the referenced item in the second list.

So Clearing it? Should just be a case of setting it to 'null' using Power Automate , right? But nope that doesn't work!

Turns out you need to set the value to -1as an Expression, e.g.,:

.... this will show the -1 like this in the Update Action:

And so NOW running the Power Automate will clear the values from the Lookup Field!

A hidden, undocumented feature - but really simple when you know it 😊