[plt-scheme] undefined value

Hi all,

Which would be the appropriate PLT Scheme value to use to represent a
NULL value in a database?

For example, in Python I'd use None, in C NULL, in Pascal nil.

The value will be part of an association list that represents a row in
a database, i.e. ((field1 . value1) (field2 . value2) ...) and will be
returned from a mzscheme extension.

I've been using 'null but that seems wrong.

I've been considering scheme_void or scheme_undefined.

I'd obviously want to be able to use an existing procedure or write
new one to checks if the value of a field is NULL.

Many thanks!

Cheers,
Dave