From 0d30c16acf9863db83837deeb8516b647c300ec0 Mon Sep 17 00:00:00 2001
From: Tommi Reiman <tommi@iki.fi>
Date: Wed, 28 Aug 2024 00:20:31 +0300
Subject: [PATCH] fix #1096

---
 CHANGELOG.md               | 1 +
 src/malli/error.cljc       | 2 +-
 test/malli/error_test.cljc | 5 +++++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 872060d8d..30f4ba57d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,7 @@ Malli is in well matured [alpha](README.md#alpha).
 * Fix ClojureScript [arithmetic warning](https://github.com/metosin/malli/issues/1093)
 * Distribute `:merge` over `:multi` [#1086](https://github.com/metosin/malli/pull/1086), see [documentation](README.md#distributive-schemas)
 * allow `m/-proxy-schema` child to be a `delay`
+* Fix `malli.dev.pretty` throws when explaining errors in nested maps [#1094](https://github.com/metosin/malli/issues/1096)
 
 ## 0.16.3 (2024-08-05)
 
diff --git a/src/malli/error.cljc b/src/malli/error.cljc
index 5310d7be6..fb4e40603 100644
--- a/src/malli/error.cljc
+++ b/src/malli/error.cljc
@@ -193,7 +193,7 @@
     (reduce (fn [acc error] (cond-> acc (accept error) (-replace-in value (:in error) (wrap error) mask))) acc errors)))
 
 (defn -masked [mask x y]
-  (cond (map? x) (reduce-kv (fn [acc k v] (let [e (find y k)] (assoc acc k (if e (-masked mask v (val e)) mask)))) y x)
+  (cond (and (map? x) (or (nil? y) (map? y))) (reduce-kv (fn [acc k v] (let [e (find y k)] (assoc acc k (if e (-masked mask v (val e)) mask)))) y x)
         (set? x) (cond-> y (not= (count x) (count y)) (conj mask))
         (sequential? x) (-fill y (count x) mask)
         :else y))
diff --git a/test/malli/error_test.cljc b/test/malli/error_test.cljc
index d9b3335f5..bcd55480e 100644
--- a/test/malli/error_test.cljc
+++ b/test/malli/error_test.cljc
@@ -758,6 +758,11 @@
                (for [error (:errors explain)]
                  (me/error-value (assoc explain :errors [error]) {::me/mask-valid-values '...}))))))
 
+    (testing "masked nested maps #1096"
+      (is (= {"foo" "foo"}
+             (-> (m/explain [:map-of :keyword [:map-of :keyword :any]] {"foo" {:bar 1}})
+                 (me/error-value {::me/mask-valid-values '...})))))
+
     (testing "custom painting of errors"
       (is (= {:EXTRA {:value "KEY", :type :malli.core/extra-key}
               :tags #{{:value "ground"} {:value "coffee"}}