[] VM production image - Customer 'Naming Series'

I am using the latest VM production image (ERPnext v7.0.42, Frappe v7.0.30)

What I find surprising is that apparently the ‘Series’ for Customers is not mandatory (while it IS mandatory in the online ERPNExt (ERPNext v7.0.40, Frappe v7.0.30) also it seems not to exist even (which surprises me because I thought it would be somehow the dabase ID of a Customer (and maybe other Documents as well)

can anyone kindly clarify on this?