what is .../log/radius/radacct/NULL

[Rich]

I have a file named NULL in  /usr/local/var/log/radius/radacct
on one of my FreeRadius servers... that keeps growing and growing...
it seems to be a binary equivalent of the csv files I am collecting.

Application is VOIP CDR collection.

It is an older version of freeradius running in a SCREEN session with 'radiusd -sfx'

Problem is I think the NULL file grows until it is too big then the radiusd task crashes.
This has happened once just recently.

I cannot find anything about it nor how to not use it.
I have 2 other FreeRadius servers running, looks like they are configured the same , 
they are running the same way...
but do not have this file showing up...

I do not see it mentioned anywhere in docs or config files.

I am currently building up an FC5 server with newest rev of freeradius,
but am having difficulty porting the sql.conf file.

Any clues would help and be appreciated.
Thanks,
Rich