title: Unexpected "null" token field when using jquery token input - how do I get rid of it?
body: <p>I followed this screencast: <a href="http://railscasts.com/episodes/258-token-fields?view=asciicast" rel="nofollow">http://railscasts.com/episodes/258-token-fields?view=asciicast</a></p>
  
  <p>As one of the steps, I added the prepopulate option as suggested and got the edit form working nicely. This is the javascript, written in coffeescript since I'm using Rails 3.1:</p>
  
  <pre><code>  $("#location_token_field").tokenInput "/person/locations.json", {
      crossDomain: false,
      prePopulate: $(this).data("pre"),
      theme: "facebook",
      preventDuplicates: true
    }
  </code></pre>
  
  <p>This is all and well except that <strong>now, in the #new action, the token input field always starts out with "null" there.</strong></p>
  
  <p>The following is the form part in question:</p>
  
  <pre><code>    &lt;div id="location_area"&gt;
          &lt;%= link_to image_tag("location_icon2.png", :size=&gt;"35x35"), "javascript:void(0)", id: "location_icon", class: "blank_button" %&gt;
          &lt;div id="location_field"&gt;
              &lt;%= f.text_field :location_tokens, id: "location_token_field", placeholder: "Where?", 
                  "data-pre" =&gt; memory.locations.map(&amp;:attributes).to_json %&gt;
          &lt;/div&gt;
      &lt;/div&gt;
  </code></pre>
  
  <p>Any ideas why this is happening / how I can solve this? I would like to keep prepopulate so the edit form is populated appropriately.</p>