handler to be a function which,
              ;; in its turn, assigns the decoded value to the
              ;; corresponding variable.  If no variable name matches
              ;; the key, the value handler is set to skip the value.
              (json:set-custom-vars
                  :object-value
                    (cond
                      ,@(loop for var in vars
                          collect
                           `((string= lisp-string ,(symbol-name var))
                             (lam