title: Graql insert query: duplicate Var objects
body: <pre><code>Var message = var().isa("message");
  insert(message).execute();
  
  Var relation = var().isa("connection")
      .rel("role1", id("existing-id"))
      .rel("role2", message);
  insert(relation).execute();
  </code></pre>
  
  <p>Executing the following creates two instances of a message.</p>
  
  <p>Is this expected? If it is, is it because I did not assign an ID, or because I have used two insert statements?</p>