title: Regex: Allow multiple emails separated by ; (semicolon) AND allow blank/empty value
body: <p>Here is my regex: </p>
  
  <pre><code>var emailsRegex = /^[\W]*([\w+\-.%]+@[\w\-.]+\.[A-Za-z]{2,4}[\W]*;{1}[\W]*)*([\w+\-.%]+@[\w\-.]+\.[A-Za-z]{2,4})[\W]*$/;
  </code></pre>
  
  <p>Currently it allows fully qualified single emails and multiple emails separated by semicolon, example:</p>
  
  <pre><code>email1@hi.com  
  email1@hi.com; email2@hi.com
  email1@hi.com; email2@hi.com; email3@hi.com
  </code></pre>
  
  <p>...are all valid.</p>
  
  <p>I want this to stay the same, but also allow blank/empty inputs. My form is flagging $invalid with a blank input field, even though the <code>required</code> attribute is not specified on the input field. </p>
  
  <p>I suspect this is because it is not passing the regex validation. Thanks!</p>