Error: You must set an element with `Modal.setAppElement(el)` to make this accessible

I get error, but CHANGELOG says:

v0.5.0 - Tue, 22 Sep 2015 19:19:44 GMT
[changed] setAppElement method is now optional.

So I'm confused.

Error: react-modal: You must set an element with `Modal.setAppElement(el)` to make this accessible
    at validateElement (index.js:224)
    at show (index.js:211)
    at Object.toggle (index.js:219)
