title: Wrap Bluebird promise in mPromise
body: <p>I am using mPromises throughout a service and in order to maintain a consistent interface (i.e end() for ex) I have a need to wrap a promisfied Bluebird function in it - I am not too familiar with mPromise though and am not succeeding. Here's what I have:</p>
  
  <pre><code>var p = new mPromise();
  p.chain(Bluebird.promisify(easypost.Address.create_and_verify, easypost.Address)(params.recipient)
      .then(function(res) {
        return p.resolve(res);
      }, function(err) {
        return p.reject(err);
      });
  )
  return p;
  </code></pre>
  
  <p>It's a but contrived but the general idea. This yields this error:</p>
  
  <pre><code>[TypeError: Cannot call method 'bind' of undefined]
  </code></pre>