Currently, there isn't a non-code way to exert control over how users add and remove rows to repeating sections.
One non-code technique you could use is to prevent the form from being submitted if it has blank rows, and display a message telling the user to delete or fill in any blank rows in the form.
Otherwise, to actually prevent adding more than one blank row, you could add your own Add Row button that uses qRules' Insert command to add rows, and disable it if the table already has a blank row.