Hi @Yoichi,
I would like to apoligize, I shouldve understood your reply and think about it further rather than respond immediately (I am a beginner in UiPath), yes you are absolutely right, I dont need to create an dt_aux since I can just put an if in the for each to run only on NULL rows. I am sorry for wasting your time, I should read and understood your reply more carefully.
Lesson Learned
Thank you @Yoichi and @supermanPunch for your time and help, its solved now!