title: Cannot read property '@global' of undefined - NPM link MUI components
body: <p>I have created a number of React components which wrap Material-UI components and are packaged as an NPM module.</p>
  
  <p>The module works fine when installed via the remote package: <code>npm install *name-of-package*</code>, or via local install: <code>npm install ../*name-of-package*</code>. </p>
  
  <p>For module development, however, I would like to use <code>npm link</code> so that I can use <code>webpack --watch</code> / <code>webpack-dev-server</code> etc in the module and site directories. </p>
  
  <p>To do so, I am running <code>npm link</code> to create a symlink in the module directory, and then <code>npm link *name-of-package*</code> in the site directory. Webpack starts as expected, however I keep encountering errors in the browser related to MUI's <code>withStyles</code> function:</p>
  
  <p><code>Uncaught TypeError: Cannot read property '@global' of undefined</code> referring to the <code>var rules = style[propKey];</code> line of the <code>function handleNestedGlobalContainerRule(rule)</code>.</p>
  
  <p>And other such as: <code>The above error occurred in the &lt;WithStyles(Typography)&gt; component</code></p>
  
  <p>From what I can tell from similar posts this is complaining about the absence of <code>theme</code> object (the site has a <code>MuiThemeProvider</code> with a theme object declared).</p>
  
  <p>Can anyone suggest why this might be working with <code>npm install</code> and not <code>npm link</code>? I cannot seem to figure this one out.</p>