net/mail: change in behavior of ParseAddressList("") in 1.15 #40803
Description
In releases of Go before 1.15, mail.ParseAddressList("") returned nil and an error mail: no address. In Go 1.15 it returns nil and a nil error. This change was due to the fix for #36959, which is not about an empty string. There's no reason to change the behavior here. We should fix this on tip and backport the fix to 1.15 for 1.15.1.