The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/4df0c19683f40fd0554edebf9db70d56bb2015b5

commit 4df0c19683f40fd0554edebf9db70d56bb2015b5
Author: Xiaochu Liu <xiaochu@chromium.org>
Date: Wed Jan 31 01:47:21 2018

platform_AddPrinter: fix dbus_send and use it

dbus_send module assumes output of dbus-send command has a non-empty
return value list. However, we do have an API that returns empty list in
Chrome on success. This CL fixes dbus_send module to return None instead
of crash-and-fail on empty list return value.

Alternate solution is to change chrome API to return a fake boolean to
get around this limitation but that fake return value causes more
confusion that benefit. This fix does not alternate any behavior of
autotests that call dbus_send (call with empty return output already
crashes).

BUG= chromium:804485 
TEST=test_that -b ${BOARD} 100.127.0.229 platform_AddPrinter.epson

Change-Id: I1756303b23c122cf2d47fdde1d8f429c88704d66
Reviewed-on: https://chromium-review.googlesource.com/891665
Commit-Ready: Xiaochu Liu <xiaochu@chromium.org>
Tested-by: Xiaochu Liu <xiaochu@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>

[modify] https://crrev.com/4df0c19683f40fd0554edebf9db70d56bb2015b5/client/common_lib/cros/dbus_send.py
[modify] https://crrev.com/4df0c19683f40fd0554edebf9db70d56bb2015b5/client/site_tests/platform_AddPrinter/platform_AddPrinter.py