[demo] Return undefined as typing

Author: jamesgpearce

site/demos/04_todo/v1.md

@@ -151,7 +151,7 @@ const NewTodo = () => {
   const handleKeyDown = useAddRowCallback(
     'todos',
     ({which, target: {value: text}}) =>
-      which == 13 && text != '' ? {text} : null,
+      which == 13 && text != '' ? {text} : undefined,
     [],
     undefined,
     () => setText(''),

site/demos/04_todo/v2.md

@@ -275,8 +275,8 @@ appears in the current IndexView component:
    const handleKeyDown = useAddRowCallback(
      'todos',
      ({which, target: {value: text}}) =>
--      which == 13 && text != '' ? {text} : null,
-+      which == 13 && text != '' ? {text, type} : null,
+-      which == 13 && text != '' ? {text} : undefined,
++      which == 13 && text != '' ? {text, type} : undefined,
 -    [],
 +    [type],
      undefined,

site/demos/04_todo/v5.md

@@ -106,7 +106,7 @@ creates a new todo:
    const handleKeyDown = useAddRowCallback(
      'todos',
      ({which, target: {value: text}}) =>
-       which == 13 && text != '' ? {text, type} : null,
+       which == 13 && text != '' ? {text, type} : undefined,
      [type],
      undefined,
 -    () => setText(''),