the value of each byte ranges from x'00' to x'ff' and is just that... a value
nullness is not a value is a concept which means the absence of something,
in this case a value
to distinguish between low values and NULL value
every field must be defined os two tokens...
a flag and a value
the flag vill tell if the value has been assigned ( NOT NULL ) or not ( NULL)
so that You can process accordingly