This only happens when you are showing data from different data types. When the columns are showing data from the same thing an empty cell will be empty because the value is ‘null’ for that cell (you can see the empty values on the demo page). If you are showing data from different data types you should make sure that the data lists have the same length, or you could group the list by a shared field.
Yes you can do this. You will have to use the ‘:formatted as text’ operator in combination with the ‘:extract with regex’ operator. I have updated the demo to include a calculation example in column 9. You can create all kind of calculations using this method. It will also allow you to alter the cell data in a particular way