BUG #16913: GENERATED AS IDENTITY column nullability is affected by order of column properties

The following bug has been logged on the website:

Bug reference: 16913
Logged by: Pavel Boev
Email address: pavel(dot)boev(at)invitae(dot)com
PostgreSQL version: 13.2
Operating system: Debian 8.3.0-6
Description:

I noticed that nullability of columns having GENERATED AS IDENTITY option is
affected by the order of NULL option, so the next query will create a
"my_table" table having non-nullable column "generated":

create table my_table (
generated integer null generated by default as identity,
data text not null
);

Whereas the following query will create a "my_table" table having nullable
column "generated":

create table my_table (
generated integer generated by default as identity null,
data text not null
);

I noticed the issue appeared in postgres 13.2, however folks say that they
bug affects versions 10, 11 and 12 as well.