>>Actually, you could leave them, and eliminate only when field is empty, i.e. normal lines would still have spaces between. Do you want to know how?
>>
>
>Yes, I do.

You place 'invisible' vertical line (color=white) besides the field so line's height covers both field height and extra space, and you mark the line the same way as the field: i.e. remove line when blank and print when...