again session class question

[eluser]EugeneS[/eluser]
hi,

lets imagine i have in session variable called "some_name" with the value "FALSE"

now my question:

how to define if such a variable exists in session or doesnt ?

as you know if some variable not registered in session, CI return me FALSE ... how to define if this is kind of VALUE OF EXISTED VARIABLE or VARIABLE WITH THIS NAME ISNT REGISTERED IN THE SESSIOn ?