Allow nil as an answer.

src/koans/maps.clj

@@ -24,6 +24,9 @@
   (= __ ({2006 "Torino" 2010 "Vancouver" 2014 "Sochi"} 2010))
 
   "You may not be able to find an entry for a key"
+  (= __ (get {:a 1 :b 2} :c))
+
+  "But you can provide your own default"
   (= __ (get {:a 1 :b 2} :c :key-not-found))
 
   "You can find out if a key is present"

src/path_to_answer_sheet.clj

@@ -44,6 +44,7 @@
                  1
                  1
                  "Vancouver"
+                 nil
                  :key-not-found
                  true
                  false

src/path_to_enlightenment.clj

@@ -3,8 +3,8 @@
   (:require [clojure.set]
             [clojure.string]))
 
-(def __ nil)
-(def ___ (fn [& args] nil))
+(def __ :fill-in-the-blank)
+(def ___ (fn [& args] __))
 
 (defmacro meditations [& forms]
   (let [pairs (partition 2 forms)]