code: public Object createDBRef(final String ns, final ObjectId id) {
          return new BasicBSONObject("$ns", ns).append("$id", id);
      }
docs: This is a factory method pattern to create appropriate objects for BSON type DBPointer(0x0c).
  
  @param ns the namespace of the reference
  @param id the identifier of the reference
  @return object to be used as reference representation