Merge pull request #35 from FannyVieira/issue-16-null-input

fix #16 missing documentation: null/undefined as input value

Author: bvaughn

content/docs/forms.md

@@ -264,6 +264,21 @@ this.setState(partialState);
 
 Also, since `setState()` automatically [merges a partial state into the current state](/docs/state-and-lifecycle.html#state-updates-are-merged), we only needed to call it with the changed parts.
 
+## Controlled Input Null Value
+
+Specifying the value prop on a [controlled component](/docs/forms.html#controlled-components) prevents the user from changing the input unless you desire so. If you've specified a `value` but the input is still editable, you may have accidentally set `value` to `undefined` or `null`.
+
+The following code demonstrates this. (The input is locked at first but becomes editable after a short delay.)
+
+```javascript
+ReactDOM.render(<input value="hi" />, mountNode);
+
+setTimeout(function() {
+  ReactDOM.render(<input value={null} />, mountNode);
+}, 1000);
+
+```
+
 ## Alternatives to Controlled Components
 
 It can sometimes be tedious to use controlled components, because you need to write an event handler for every way your data can change and pipe all of the input state through a React component. This can become particularly annoying when you are converting a preexisting codebase to React, or integrating a React application with a non-React library. In these situations, you might want to check out [uncontrolled components](/docs/uncontrolled-components.html), an alternative technique for implementing input forms.

static/_redirects

@@ -1 +1,2 @@
-/html-jsx.html  http://magic.reactjs.net/htmltojsx.htm  301
+/html-jsx.html  http://magic.reactjs.net/htmltojsx.htm  301
+/tips/controlled-input-null-value.html  /docs/forms.html#controlled-input-null-value