def nil_uuid?
      return false if self.time_low != 0
      return false if self.time_mid != 0
      return false if self.time_hi_and_version != 0
      return false if self.clock_seq_hi_and_reserved != 0
      return false if self.clock_seq_low != 0
      self.nodes.each do |node|
        return false if node != 0
      end
      return true
    end
def nil_uuid?
      return false if self.time_low != 0
      return false if self.time_mid != 0
      return false if self.time_hi_and_version != 0
      return false if self.clock_seq_hi_and_reserved != 0
      return false if self.clock_seq_low != 0
      self.nodes.each do |node|
        return false if node != 0
      end
      return true
    end
Returns true if this UUID is the
 nil UUID (00000000-0000-0000-0000-000000000000).