(nil? x)
Returns true if x is nil, false otherwise.
user=> (nil? nil)
true
user=> (nil? 0)
false
user=> (nil? false)
false
user=> (nil? '())
false
;; as nil? is defined as "Returns true if x is nil, false otherwise."
;; and some? is defined as "Returns true if x is not nil, false otherwise."
;; (some? x) is just shorthand for (not (nil? x))
;; this also means that nil? is the same as (not (some? x)) as this
;; just expands into (not (not (nil? x))).
(def nil?? (complement some?))
;;#'user/nil??
(for [x [nil 0 false [] '()]]
(= (nil? x) (nil?? x)))
;;=> (true true true true true)