title: TypeError: Attempted to wrap undefined property as function
body: <p>The example below is simplified. I have a getter method:</p>
  
  <pre><code>class MyClass {
    constructor() {}
    get myMethod() {
      return true;
    }
  }
  </code></pre>
  
  <p>which is processed by babel. And I want to mock it like this:</p>
  
  <pre><code>var sinon = require('sinon');
  var MyClass = require('./MyClass');
  var cls = new MyClass();
  
  var stub = sinon.stub(cls, 'myMethod');
  stub.returns(function() {
    return false;
  });
  </code></pre>
  
  <p>But I get the following error:
  <code>TypeError: Attempted to wrap undefined property myMethod as function</code></p>
  
  <p>And this happens on both version 1 and 2 of sinon library.</p>