title: How do you check if an embedded document exists in a document in mongoid?
body: <p>How do you check if an embedded document exists for a document using mongoid in Ruby on Rails?  Say I have a document <code>user</code> that has <code>name</code>, <code>email</code>, and might have a <code>nicknames</code> embedded document.  Right now if I run <code>user.first.nicknames</code> and if that <code>user</code> doesn't have the <code>nicknames</code> embedded document in it, it will error out. I've tried <code>matches?</code> and <code>exists?</code> but they don't work. </p>
  
  <p>Thanks!</p>