title: Request header field If-None-Match is not allowed by Access-Control-Allow-Headers in preflight response
body: <p>I am receiving the following error when posting to a REST API using     <code>dojo/store/JsonRest</code>.
  I am using <code>"X-Requested-With": null</code> in order to avoid preflight request but I still receive this error.</p>
  
  <p>API fully support CORS.</p>
  
  <p>Any idea how can be fixed?</p>
  
  <blockquote>
    <p>Request header field If-None-Match is not allowed by
    Access-Control-Allow-Headers in preflight response.</p>
  </blockquote>
  
  <pre><code>        var store = new JsonRest({
              target: 'https://api.xxx.com/data',
              headers: {
                  "Authorization": 'Bearer ' + 'd4c72611fc43ab44a46344d907a2b96964df2c91',
                  "X-Requested-With": null // no prefligh
              }
          });
          store.get('1-00').then(function (data) {
              // ok works here
              console.log('get', data)
          });
          // post request
          store.add({name:'test'}).then(function (data) {
              // error here
              console.log('add', data)
          });
  </code></pre>