What is the right way to clear select2 dropdown?

HTML

<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/select2/4.0.1/css/select2.min.css">
<script src="//cdnjs.cloudflare.com/ajax/libs/select2/4.0.1/js/select2.min.js"></script>
<link rel="stylesheet" href="https://select2.github.io/css/s2-docs.css">
<select id="StreamName">
  <option value="3620194" selected="selected">select2/select2</option>
</select>
<div class="testing">
  <button id="set-null">
    Set Null
  </button>
</div>

CSS

#StreamName {
  width: 90%
}

.testing {
  margin-top: 20px;
}

JavaScript

$(document).ready(function() {
  $("#StreamName").select2({
    ajax: {
      url: "https://api.github.com/search/repositories",
      dataType: 'json',
      delay: 250,
      data: function(params) {
        return {
          q: params.term, // search term
          page: params.page
        };
      },
      processResults: function(data, params) {
        // parse the results into the format expected by Select2
        // since we are using custom formatting functions we do not need to
        // alter the remote JSON data, except to indicate that infinite
        // scrolling can be used
        params.page = params.page || 1;

        return {
          results: data.items,
          pagination: {
            more: (params.page * 30) < data.total_count
          }
        };
      },
      cache: true
    },
    escapeMarkup: function(markup) {
      return markup;
    }, // let our custom formatter work
    minimumInputLength: 1,
    templateResult: formatRepo, // omitted for brevity, see the source of this page
    templateSelection: formatRepoSelection // omitted for brevity, see the source of this page
  });


  //$("#StreamName").val(null).trigger("change");

  // For testing...
  $('#set-null').click(function() {
    $("#StreamName").val(null).trigger("change");
  });



});


function formatRepo(repo) {
  if (repo.loading) return repo.text;

  var markup = "<div class='select2-result-repository clearfix'>" +
    "<div class='select2-result-repository__avatar'><img src='" + repo.owner.avatar_url + "' /></div>" +
    "<div class='select2-result-repository__meta'>" +
    "<div class='select2-result-repository__title'>" + repo.full_name + "</div>";

  if (repo.description) {
    markup += "<div class='select2-result-repository__description'>" + repo.description + "</div>";
  }

  markup += "<div class='select2-result-repository__statistics'>" +
    "<div class='select2-result-repository__forks'><i class='fa fa-flash'></i> " + repo.forks_count + "...