Fix a false negative in `map-elt' with alists and values being nil

* lisp/emacs-lisp/map.el (map-elt): If map is an alist and key is
found but its associated value is nil, do not return the default
value.

* test/automated/map-tests.el: Add a regression test.

1 files changed, 6 insertions, 0 deletions

diff --git a/test/automated/map-tests.el b/test/automated/map-tests.el
index 5201116613e..e65af894275 100644
--- a/test/automated/map-tests.el
+++ b/test/automated/map-tests.el
@@ -66,6 +66,12 @@ Evaluate BODY for each created map.
   (with-maps-do map
     (assert (= 5 (map-elt map 7 5)))))
 
+(ert-deftest test-map-elt-with-nil-value ()
+  (assert (null (map-elt '((a . 1)
+                           (b))
+                         'b
+                         '2))))
+
 (ert-deftest test-map-put ()
   (with-maps-do map
     (map-put map 2 'hello)