def read_binary_null_type(length)
      case length
      when 0  then 0 # null byte
      when 8  then CFBoolean.new(false)
      when 9  then CFBoolean.new(true)
      when 15 then 15 # fill type
      else
        raise CFFormatError.new("unknown null type: #{length}")
      end
    end
def read_binary_null_type(length)
      case length
      when 0  then 0 # null byte
      when 8  then CFBoolean.new(false)
      when 9  then CFBoolean.new(true)
      when 15 then 15 # fill type
      else
        raise CFFormatError.new("unknown null type: #{length}")
      end
    end
read a „null” type (i.e. null byte, marker byte, bool value)