Wynnded posted a good workaround idea. Just to expand on it a bit, I found that you cannot leave the phone number field blank. When a call comes in, the caller ID feature on your phone attempts to display a number. When the number is unavailable or restricted, then this is what appears in the phone number field. I found that in order for this workaround to be effective, create your Google contacts (one for Restricted and one for unavailable) with the word Restricted and/or Unavailable in the phone number field. Then follow the remaining steps to add that contact to your auto-reject list.