Update ExampleTodoList.md (reduxjs#1852)

janhenrikoverland · timdorr · commit 8636df83a68c · 2016-07-18T23:53:18.000-04:00
Calling todo(undefined, action) does not work without the default state value.
diff --git a/docs/basics/ExampleTodoList.md b/docs/basics/ExampleTodoList.md
@@ -58,7 +58,7 @@ export const toggleTodo = (id) => {
 #### `reducers/todos.js`
 
 ```js
-const todo = (state, action) => {
+const todo = (state = {}, action) => {
   switch (action.type) {
     case 'ADD_TODO':
       return {
