Error log: https://pantheon.corp.google.com/errors/CIalybXDxJKDdA?time=P1D&filter=AssertionError&refresh=off&project=findit-for-me

Stack trace:
AssertionError
at _EstimateSwarmingIterationTimeout (/base/data/home/apps/s~findit-for-me/waterfall-backend:14839-f7d41cf.408837037076478115/services/flake_failure/run_swarming_util.py:61)
at CalculateRunParametersForSwarmingTask (/base/data/home/apps/s~findit-for-me/waterfall-backend:14839-f7d41cf.408837037076478115/services/flake_failure/run_swarming_util.py:125)
at RunImpl (/base/data/home/apps/s~findit-for-me/waterfall-backend:14839-f7d41cf.408837037076478115/pipelines/flake_failure/determine_approximate_pass_rate_pipeline.py:118)
at run (/base/data/home/apps/s~findit-for-me/waterfall-backend:14839-f7d41cf.408837037076478115/gae_libs/pipelines.py:297)
at evaluate (/base/data/home/apps/s~findit-for-me/waterfall-backend:14839-f7d41cf.408837037076478115/infra_api_clients/../third_party/pipeline/pipeline.py:2207)

Root cause:
A bug in flake_test_results cause the number of passes was incorrectly set to None.