fix end, last, beginning, and first to work on nil

CHANGES.md

@@ -5,6 +5,7 @@
 * Added `selected-any?` operation that returns true if any element is navigated to.
 * Huge performance improvements to `select`, `select-one`, `select-first`, and `select-one!`
 * Added META navigator (thanks @aengelberg)
+* Bug fix: END, BEGINNING, FIRST, and LAST now work properly on nil
 
 ## 0.11.1
 * More efficient inline caching for Clojure version, benchmarks show inline caching within 5% of manually precompiled code for all cases

src/clj/com/rpl/specter/impl.cljx

@@ -479,6 +479,12 @@
   (prepend-all [structure elements]))
 
 (extend-protocol AddExtremes
+  nil
+  (append-all [_ elements]
+    elements)
+  (prepend-all [_ elements]
+    elements)
+
   #+clj clojure.lang.PersistentVector #+cljs cljs.core/PersistentVector
   (append-all [structure elements]
     (reduce conj structure elements))
@@ -567,6 +573,9 @@
 
 
 (extend-protocol FastEmpty
+  nil
+  (fast-empty? [_] true)
+
   #+clj clojure.lang.IPersistentVector #+cljs cljs.core/PersistentVector
   (fast-empty? [v]
     (= 0 (vec-count v)))

test/com/rpl/specter/core_test.cljx

@@ -1191,3 +1191,8 @@
        (first (select s/META (with-meta v meta-map)))
        (first (select s/META (setval s/META meta-map v))))))
 
+
+(deftest beginning-end-on-nil
+  (is (= [2 3] (setval s/END [2 3] nil) (setval s/BEGINNING [2 3] nil)))
+  (is (nil? (setval s/FIRST :a nil)))
+  )