chickadee » spiffy-request-vars » nonempty

A combinator to be used with converters. Returns the converter value if the variable is set and its value is not null. Returns #f if its value is null.

It can be useful for handling values from form-submited data, when all form fields are submited, but some are null. If you are only interested in values that are not null, you can just check if the return value of nonempty is not #f (otherwise you'd have to check if the variable was actually in the request and if its value is not null).

Example:

(let ((var (or ($ 'var (nonempty as-string)) "not set")))
   var)