[Samba] Updating to Samba-4.6.0 testparm ERROR: Invalid idmap range for domain *!

[spindles7]

After updating my test AD DC from samba version 4.5.5 to 4.6.0 and running testparm as asvised, I get the error

idmap range not specified for domain '*'
ERROR: Invalid idmap range for domain *!

After I get trhe dump of the service definitions, I notice that there is a line in the [global] section:

	idmap config * : backend - tdb

However, my smb.conf doesn't contain any such line (as recommended by the Wiki documentation) so where is this coming from, and what
to do about it?

Thanks,

Roy