title: How do I set a blank value for an f.select form field
body: <p>I am using the following to allow my users to select their sex in their profile. </p>
  
  <pre><code>&lt;%= f.select (:sex, %w{ Male Female }) %&gt;
  </code></pre>
  
  <p>How would I create a blank value that the list would default to if nothing has been passed to the user.sex column? I am simply passing male or female as a string. </p>
  
  <p>The purpose is I want a blank value so a validation can make sure they are aware they have to select it. </p>