title: Nullable Enum helper for having a default value
body: <p>I recently made an extension for binding a dropdownlist to a model,
  Unfortunately I couldn't make the -wanna be default- <strong>"please select..."</strong> be selected as default
  Always the dropdown's index is 1 and it selects the Enum's 1st item as the default item.
  I made the extension based on <a href="https://stackoverflow.com/a/18248755/50506">this</a> -Darin's great answer-</p>
  
  <p>I get advised to use <strong>nullable enum</strong>,
  I couldn't make it work yet, hope get a help on it</p>
  
  <p>The specification of the default selection text in the helper:</p>
  
  <pre><code>return htmlHelper.DropDownListFor(expression, items, "Please select ...");
  </code></pre>
  
  <p>How to make the "please select..." selected as default in any dropdowns.</p>
  
  <p>In the ViewModel I used:</p>
  
  <pre><code>public TimePlan? TimeList { get; set; }
  </code></pre>