title: Spark Kryo Exception - Class is not registered: com.google.common.base.Present
body: <p>I am using Spark 1.6.0-cdh5.8.0.</p>
  
  <p>I'm trying to use Kryo.  I have guava Optional because I thought that's what spark was using.</p>
  
  <p>However I cannot serialize that using Kryo because Present class has default-visibility.</p>
  
  <p>So...has anyone come across this and solved it.</p>
  
  <p>The following code does not work since Present is hidden...</p>
  
  <pre><code>kryo.register(com.google.common.base.Present.class)
  </code></pre>