I was working on a power automate where I needed to check if a value is null or not then update look up values. One option was to check in every if/else statement but thats too messy and lengthy.
You can check this one line of code in your look up
if(empty(variables('Resolution')), ' ',concat(variables('Resolution')))
In above example, first I stored my look up value in a variable to make it simple, you can use your attribute here directly if you need to.