The default is currently zero, which causes chaos if the employee is not set up.
It is a legal requirement to pay HP so should either be mandatory fields or even better default rate 8%/4 weeks
Unfortunately we tread a thin line with the regulators in each country around what constitutes "advice" so we are unable to set default values in many areas of our product.
That said, Reckon Accounts does have default payroll preferences you may not be aware of where you can set these for defaults yourself.
Simple go to Edit > Preferences > Payroll & Employees > Employee defaults > Leave details..