The CQ run got a 502 error on https://chromiumos-cl-scanner.appspot.com/external/risk/build/2250292
(see  issue 806687 )
but then the report_stages cbuilbot python code died on :
  File "/b/c/cbuild/repository/chromite/cbuildbot/stages/generic_stages.py", line 701, in Run
    self.PerformStage()
  File "/b/c/cbuild/repository/chromite/cbuildbot/stages/report_stages.py", line 1050, in PerformStage
    self._RunRiskReport()
  File "/b/c/cbuild/repository/chromite/cbuildbot/stages/report_stages.py", line 1070, in _RunRiskReport
    for link_text, url in sorted(report.iteritems()):
AttributeError: 'str' object has no attribute 'iteritems'

As logged in :
https://logs.chromium.org/v/?s=chromeos%2Fbb%2Fchromeos%2Fmaster-paladin%2F17607%2F%2B%2Frecipes%2Fsteps%2FReport%2F0%2Fstdout

This is likely the previous exception trickling down, but we can probably make this code more robust by checking whether GetCLRiskReport() has returned an error string rather than the result dictionary.