title: Exclude a module from webpack bundle
body: <p>I'd like the same functionality like RequireJS <code>empty:</code> <a href="http://requirejs.org/docs/optimization.html#empty">http://requirejs.org/docs/optimization.html#empty</a></p>
  
  <p>My use-case is that I include <code>jquery-migrate</code> in development, but I'd like to exclude this when built for production.</p>
  
  <p>Using <code>IgnorePlugin</code> just makes it not included, and when <code>require</code>ing it in the code, it then throws an error (<code>Uncaught Error: Cannot find module "jquery-migrate"</code>).</p>
  
  <p>What I'd like to happen is for it to just return undefined, or something of the like (like <code>empty:</code> in RequireJS). Id like to not touch the import in the code, just configuring it to return <code>undefined</code>.</p>
  
  <p>EDIT: Using <code>NormalModuleReplacementPlugin</code> works, if I point the replacement to an empty file. But keeping an empty file around just for this seems unnecessary.</p>