Проверка на существование ключей в таблице

(defparameter *my-hash* (make-hash-table))
; *MY-HASH*
(setf (gethash 'entry *my-hash*) nil)

(if (nth-value 1 (gethash 'entry *my-hash*))
    "Key exists"
    "Key does not exist")
; "Key exists"

(if (nth-value 1 (gethash 'no-entry *my-hash*))
    "Key exists"
    "Key does not exist")
; "Key does not exist"