dnszone_add requires the serial but freeipa no longer allows this to be supplied

[DeathRabbit679]

If I make a call to freeipa(4.9.11) like the following:

ipa_conn.dnszone_add(a_idnsname="foo.bar.com.", o_idnssoaserial=1234, o_idnssoarname="hostmaster", o_idnssoamname="myipa.bar.com.")

I get back an error message from freeipa saying:

invalid 'serial': this option is deprecated

It looks like, at some point, freeipa switched over to managing the serial number more directly, making it immutable from the user perspective. However, o_idnssoaserial is a required positional argument for the function, so I can't not supply it to the function call. A workaround is to pass in None for this required argument.