ASCII NUL in NAS-Filter-Rule

[Ruslan Pustovoytov]

Hi All

My nas box can use attribute NAS-Filter-Rule from radius server to 
construct filter rules per subscriber "on the fly".
Accodingly to rfc 4849 this attribute should contain ascii NUL (0x00) as 
a delimiter between individual filter rules and at the end of rules.
Freeradius define this attribute as a string and I do not know how to 
create valid string with nul character.
I changed attribute type to octets and successfully add null character 
but a whole string converted to hex also and attribute was not readable.
How to send nul character without changing attribute type ?