looking at autoupdate_EndToEndTest.paygen_au_canary_delta on Samus, 
I stumble upon a number of test failure with the signature:
"Unhandled TypeError: expected string or buffer"

SQL query: `test_name` = 'autoupdate_EndToEndTest.paygen_au_canary_delta' and `job_started_time` >= '2016/03/27' and `status` = 'FAIL'

For instance:
http://cautotest.corp.google.com/afe/#tab_id=view_job&object_id=56764074

More recently:
http://cautotest.corp.google.com/afe/#tab_id=view_job&object_id=58112166