title: fill method in CasperJS
body: <p>I would like to fill a form and submit it.</p>
  
  <p>check a part of my script :</p>
  
  <pre class="lang-js prettyprint-override"><code>casper.then(function(){
      if(this.exists('#msisdn')){
          this.echo('ok found');
          **this.test.assertExists('form[id="internetPlus"]', 'form is found');
          this.fill('form[id="internetPlus"]', {
              'numero': 'xxxxxxxx'  
          },true);**
          this.click('#button');
  </code></pre>
  
  <p>And I got this error :</p>
  
  <pre><code>**PASS form is found**
  [info] [remote] attempting to fetch form element from selector:   
  'form[id="internetPlus"]'
  **[error] [remote] TypeError: 'undefined' is not an object (evaluating   
  'field.getAttribute')
  FAIL CasperError: Unable to fill form
  #    type: uncaughtError
  #    error: "CasperError: Unable to fill form"
  CasperError: Unable to fill form                                               
    /home/soufyan/workspace/casperjs:524 in fill
    /home/soufyan/workspace/casperjs/kkostoreHomeTest.js:45
    /home/soufyan/workspace/casperjs:909 in runStep
    /home/soufyan/workspace/casperjs:252 in checkStep**
  </code></pre>
  
  <p>I don't understand why i'm unable to fill form because the assert result is OK.</p>