go/svc/invoice: polishify
diff --git a/go/svc/invoice/render.go b/go/svc/invoice/render.go
index 47c6c6d..a433fa8 100644
--- a/go/svc/invoice/render.go
+++ b/go/svc/invoice/render.go
@@ -72,7 +72,10 @@
 		InvoiceeBilling: make([]string, len(i.CustomerBilling)),
 	}
 
-	unit := "€"
+	unit := i.Unit
+	if unit == "" {
+		unit = "€"
+	}
 
 	for d, s := range i.InvoicerBilling {
 		data.InvoicerBilling[d] = s