We have an alert/regression here
https://crosland.corp.google.com/log/11048.0.0..11051.0.0

probably due to
https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/1208899/3/client/cros/power/power_utils.py

Need to restore "None" now.

		ERROR	graphics_VideoRenderingPower	graphics_VideoRenderingPower	timestamp=1536720890	localtime=Sep 11 19:54:50	Unhandled TypeError: %d format: a number is required, not NoneType
  Traceback (most recent call last):
    File "/usr/local/autotest/common_lib/test.py", line 634, in _exec
      _cherry_pick_call(self.cleanup, *args, **dargs)
    File "/usr/local/autotest/common_lib/test.py", line 715, in _cherry_pick_call
      return func(*p_args, **p_dargs)
    File "/usr/local/autotest/tests/graphics_VideoRenderingPower/graphics_VideoRenderingPower.py", line 58, in cleanup
      self._backlight.restore()
    File "/usr/local/autotest/cros/power/power_utils.py", line 409, in restore
      self.set_level(self._init_level)
    File "/usr/local/autotest/cros/power/power_utils.py", line 352, in set_level
      self._try_bl_cmd('--set_brightness=%d' % (level))
  TypeError: %d format: a number is required, not NoneType