Expanding undefined variables within a shell

[Regid Ichira <regid23@yahoo.com>]

  Within a shell, what is the difference between [ -n undefinedString ] and [ -n "$undefinedString" ] ?
With bash I get:

    $ unset undefinedString
    $ [ -n undefinedString ]  &&  printf "$undefinedString" | od -c
    0000000
    $ [ -n "$undefinedString" ]  &&  printf "$undefinedString" | od -c
    $ [ -z "$undefinedString" ]  &&  printf "$undefinedString" | od -c
    0000000


I mean, shouldn't [ -n undefinedString ], which I guess is without shell expansion, give an error?  Clearly
it is an empty string.

  I think I am confusing various terms.  An explanation, perhaps by using the concept of C like strings,
might be helpful.