title: Select2 Default selected from optgroup
body: <p>Need some help here. I inherited this code and I am not 100% on what needs to be done here but I need to set the default selected item to be the first group/first option instead of the <code>data-placeholder</code>. 
  I tried using <code>ng-init</code> but I wasn't able to get it to work. 
  How can I achieve this with the below code?</p>
  
  <pre><code>&lt;div ng-repeat='searchField in searchFields.device'&gt;
      &lt;select data-placeholder='Search Field' ng-model='searchField[0]' ui-select2&gt;
          &lt;option value=''&gt;&lt;/option&gt;
          &lt;optgroup label='FooGroup1'&gt;
              &lt;option value='foo_option1'&gt;foo_option1&lt;/option&gt;
          &lt;/optgroup&gt;
          &lt;optgroup label='FooGroup2'&gt;
              &lt;option value='foo_option1'&gt;foo_option1&lt;/option&gt;
              &lt;option value='foo_option1'&gt;foo_option1&lt;/option&gt;
          &lt;/optgroup&gt;
      &lt;/select&gt;
  ....
  </code></pre>
  
  <p><strong>ACTUAL HAML</strong></p>
  
  <pre><code>%div(ng-repeat="searchField in searchFields.message")
    %select(ng-model="searchField[0]" ui-select2 data-placeholder="Search Field" ng-init="searchField[0] = ")
      %option(value="")
      - devices_optgroup.each do |group, attrs|
        %optgroup{label: group}
          - attrs.each do |attr, label|
            %option(value="#{attr}")= label
  </code></pre>