title: $_FILES returns empty when using HTML Form and Dropzone JS
body: <p>I have spent way too much time on this and browsed various questions/answers here on stackoverflow.</p>
  
  <p>I am using <a href="http://www.dropzonejs.com/" rel="nofollow noreferrer">dropzone.js</a> to add a basic drag and drop upload feature to our HTML/PHP form.  The drag and drop is working great however when the form is submitted or a file is uploaded the $_FILES returns empty and I cant figure it out.</p>
  
  <p>I checked a <a href="http://www.startutorial.com/articles/view/how-to-build-a-file-upload-form-using-dropzonejs-and-php" rel="nofollow noreferrer">tutorial</a> and no luck, also checked some <a href="https://stackoverflow.com/questions/21940099/php-files-array-is-empty">Q &amp; A's</a> from <a href="https://stackoverflow.com/questions/21047587/dropzone-form-validation">stackoverflow</a> before <a href="https://stackoverflow.com/questions/16209584/dropzone-js-files-is-empty">posting</a> here but nothing has helped.</p>
  
  <p>Here is the form in its simplest form:</p>
  
  <pre><code>&lt;form action="&lt;? echo BASE_URL; ?&gt;/process-uploads.php" method="POST" class="form-signin" role="form" enctype="multipart/form-data"&gt;
  
          &lt;div class="upload_container dropzone"&gt;Drag &amp; drop file here or
  
                  &lt;div class="fallback"&gt;
                      &lt;input name="ad" type="file" /&gt;
                  &lt;/div&gt;
              &lt;/div&gt;&lt;!--fileUpload btn btn-primary--&gt;
  
          &lt;div class="dropzone-previews"&gt;&lt;/div&gt;
  
                  &lt;input class="btn btn-lg btn-primary btn-block btn-forward" style="background:#00a85a;" type="submit" name="submit" value="Next Step" /&gt;
              &lt;/form&gt;
  </code></pre>
  
  <p>The JS is:</p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
  
  var myDropzone = new Dropzone(".dropzone", { 
      url: "&lt;? echo BASE_URL; ?&gt;/process-uploads.php/",
      paramName: "ad",
      addRemoveLinks: true,
      //maxFiles: 1,
      autoProcessQueue: false,
      //uploadMultiple: false,
      acceptedFiles: "image/png",
      dictInvalidFileType: "This file type is not supported.",
  
  });
  &lt;/script&gt;
  </code></pre>
  
  <p>And process-upload.php just checks to see if anything was sent, but returning empty:</p>
  
  <pre><code>&lt;?php
  
  if (!empty($_FILES)) {
  
      echo 'We have a file';
  
      if($_FILES['ad']) {
          echo 'We grabbed the ad&lt;br /&gt;';
  
          echo '&lt;pre&gt;';
          var_dump($_FILES);
          echo '&lt;/pre&gt;';
      }
  }
  ?&gt;
  </code></pre>
  
  <p>Any help would be greatly appreciated. For reference I already checked enyo's tutorial for <a href="https://github.com/enyo/dropzone/wiki/Combine-normal-form-with-Dropzone" rel="nofollow noreferrer">combining a form with dropzone and php</a></p>