post leaves out form variables with empty values

I traced a problem in my server to the following fact: As the example 
below will show, if you create a fillout-form which gets some 
strings, and the user leaves some fields blank when filling it out, 
the query-alist passed to the response function *leaves out* the 
variables for which no values were entered, as opposed for example to 
including the variables with null strings as their value.

(defmethod show-form ((url url:http-form) stream)
   (http:with-successful-response (stream :html)
     (html:with-fillout-form (:post url :stream stream)
       (html:accept-input 'html:string "v1" :stream stream)
       (html:accept-input 'html:string "v2" :stream stream)
       (html:accept-input 'html:submit-button "Submit" :stream stream))))

(defmethod get-form ((url url:http-form) stream query-alist)
   (http:with-successful-response (stream :html)
     (write query-alist :stream stream)))

(http:export-url #u"/test.html"
                  :html-computed-form
                  :form-function #'show-form
                  :response-function #'get-form)

I understand that makes the POST a little smaller, but for my 
purposes I want all the form variables to appear in the query-alist. 
How can this be done?

    Thanks,

	Mark


-- 
Mark Klein
Principal Research Scientist
Massachusetts Institute of Technology
77 Massachusetts Avenue, NE20-336
Cambridge MA 02139 USA
[email protected]