title: How to show avatar only if it exists?
body: <p>Is there any function in Wordpress that allows to hide the gravatar if id doesn't exists? </p>
  
  <p>I have many authors that doesn't have a gravatar and all are displayed like this:</p>
  
  <pre><code>http://prntscr.com/98zsji    
  </code></pre>
  
  <p>I would like to hide the default image.</p>
  
  <p>I used the function <code>validate_gravatar($email);</code>, but it generated an error: </p>
  
  <pre class="lang-none prettyprint-override"><code>Fatal error: Call to undefined function validate_gravatar()
  </code></pre>
  
  <p>If I print <code>$user_email</code> it display correctly the user email.</p>