ASCII NUL in NAS-Filter-Rule

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 ?