nw reactjs requring in multiple files does not work

problem-

var React= require('react')
var SomeComponent= require('./utils/SomeComponent')
var Wrapper= React.createClass({
    render: function(){
        return <SomeComponent/>
    }
})

//utils/SomeComponent.js:
var React= require('react')
module.exports= React.createClass({ 
    //..
})

throws- Error: Invariant Violation: Wrapper.render(): A valid ReactComponent must be returned. You may have returned undefined, an array or some other invalid object.

no errors when used in one file

(by the way

var React= require('react')

throws ReferenceError: document is not defined

after lot of googling I solved that by calling

global.document= window.document
global.navigator= window.navigator

Maybe it's related?)