Update 50_StoreMapping.md

www/src/pages/docs/50_StoreMapping.md

@@ -250,7 +250,7 @@ val storedPerson = storeOf<Person?>(null, job = Job())
 storedPerson.data.render { person ->
     if (person != null) { // Avoid NullPointerExceptions reading or updating storedPerson
                           // by manually creating a safe scope ensuring that person is not null
-        val storedName = customerStore.map(Person.name())
+        val storedName = storedPerson.map(Person.name())
         input {
             value(storedName.data)
             changes.values() handledBy storedName.update
@@ -1035,4 +1035,4 @@ straight-forward manner.
 
 For real world application we encourage you to apply better [structure](/docs/render/#structure-ui) and divide the UI
 into smaller and reusable parts, of course.
-:::
+:::