title: what does "Object.assign() does not throw on null or undefined source values" mean?
body: <p>I read this on <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign" rel="nofollow noreferrer">mozilla</a></p>
  
  <blockquote>
    <p>"Object.assign() does not throw on null or undefined source values" </p>
  </blockquote>
  
  <p>When I try it on <a href="http://jsbin.com/bafuyicice/edit?html,js,console" rel="nofollow noreferrer"><code>jsbin</code></a>, it seems not work.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var obj1 = {p: null};
  var obj2 = {p: "new"};
  
  console.log(_.assign(obj1, obj2));
  console.log(_.merge(obj1, obj2));
  console.log(Object.assign(obj1, obj2));</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;head&gt;
    &lt;meta charset="utf-8"&gt;
    &lt;meta name="viewport" content="width=device-width"&gt;
    &lt;title&gt;JS Bin&lt;/title&gt;
    &lt;script src="https://cdn.jsdelivr.net/lodash/4/lodash.min.js"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
  
  &lt;/body&gt;
  &lt;/html&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>can anybody help me to explain why? tks for any reply~</p>