Power Automate update/remove first blank row in Excel

Hey,

I'm creating some Power Automate flows, combined with some msForms and populate my data in an Excel sheet table.

The reason why I need an Excel sheet is because I'm also using some formulas on other sheets which use the raw data I get from the msForm.

However, I'm stuck on something and cannot figure it out. 

I have an condition where I check if a value is empty:

The 'empty' formula is as followed: 

empty(items('Apply_to_each')?['Key'])

Next, I want to do one of two things. Either remove this empty row and afterwards add the row for the msForms data, or (preferably) update this empty row to contain the data from msForms.

However, when I use "null" or "empty" as a "Key value" for "Update a row", I get the error that the Key ID cannot be null or empty. 

How can I do this, anyone who can help me with this?