https://stainless.corp.google.com/browse/chromeos-autotest-results/213661623-chromeos-test/chromeos4-row9-rack9-host5/

Job reporter cannot handle default value of execution-tag properly, and results in an exception. Not sure how much impact of this.

job_reporter: 2018-07-02 13:54:36,313:DEBUG:eventlib:run_event_command:90:Starting event command with ['/opt/infra-tools/usr/bin/lucifer_run_job', '-autotestdir', '/usr/local/autotest', '-abortsock', '/usr/local/autotest/leases/213661623.sock', '-hosts', u'chromeos4-row9-rack9-host5', '-x-level', 'STARTING', '-resultsdir', '/usr/local/autotest/results/213661623-chromeos-test/chromeos4-row9-rack9-host5', '-x-control-file', '/usr/local/autotest/results/213661623-chromeos-test/chromeos4-row9-rack9-host5/lucifer/control_attach', '-x-execution-tag', None, '-x-job-owner', u'chromeos-test', '-x-job-name', u'veyron_minnie-release/R69-10837.0.0/sanity/dummy_PassServer.sanity', '-x-reboot-after', 'never', '-x-parsing-only', '-x-run-reset', '-x-test-retries', '0', '-x-require-ssp']
Traceback (most recent call last):
  File "/usr/lib/python2.7/runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/usr/local/autotest/venv/lucifer/cmd/job_reporter.py", line 209, in <module>
    sys.exit(main(sys.argv))
  File "/usr/local/autotest/venv/lucifer/cmd/job_reporter.py", line 46, in main
    ret = _main(args)
  File "/usr/local/autotest/venv/lucifer/cmd/job_reporter.py", line 93, in _main
    return _run_autotest_job(args)
  File "/usr/local/autotest/venv/lucifer/cmd/job_reporter.py", line 106, in _run_autotest_job
    ret = _run_lucifer_job(handler, args, job)
  File "/usr/local/autotest/venv/lucifer/cmd/job_reporter.py", line 148, in _run_lucifer_job
    event_handler=event_handler, args=command_args)
  File "/usr/local/autotest/venv/lucifer/eventlib.py", line 91, in run_event_command
    with subprocess32.Popen(args, stdout=PIPE) as proc:
  File "/usr/local/google/home/chromeos-test/.cache/cros_venv/venv-2.7.6-a234a83456f26d726445fc6c8e6ce271/local/lib/python2.7/site-packages/subprocess32.py", line 825, in __init__
    restore_signals, start_new_session)
  File "/usr/local/google/home/chromeos-test/.cache/cros_venv/venv-2.7.6-a234a83456f26d726445fc6c8e6ce271/local/lib/python2.7/site-packages/subprocess32.py", line 1396, in _execute_child
    restore_signals, start_new_session, preexec_fn)
TypeError: coercing to Unicode: need string or buffer, NoneType found

Please note the value of '-x-execution-tag' is None.