title: can Google c2dm server send empty registration Id in any case?
body: <p>I am trying to send a push notification to a phone number through the c2dm server. for that to happen, I am registering my mobile with the c2dm server and i store the registration id which is got from the c2dm server.</p>
  
  <p>I am aware of the error codes like 403, 500 </p>
  
  <p>Is there any case where my registration Id could be empty? </p>