EXTFLD does not preserve null indicator

V5R4

H ALWNULL(*USRCTL)
D long_ds e ds extname(employee)
D date_of_birth e extfld(dob)

The external file EMPLOYEE was created with SQL, and the column DOB is
NULL CAPABLE. Created with an RPG-friendly short name, but prefer the
longer name. There doesn't seem to be a way to tell RPG to use the long
name, so I figured I'd just do some renames.

Unfortunately, the new field DATE_OF_BIRTH is not null capable, which
rather throws a monkey-wrench into the plans. Ultimately, I wanted to
use this to pass a record around as a parameter in several subprocedures.

I see no mention of null dropping in the manual's EXTFLD section (p.350)
Likewise, I see no mention of dropping the null-capable attribute in
the Database Null Value Support section (p.257)

Is this working as intended? If so, I'll drop a line to the
documentation people to get the manual adjusted. If it is working as
intended,is the basic answer that I can't rename subfields in an
externally defined DS, and that the database guy ought to stick to 10
characters like we always did in the past?
--buck