What is the bug or feature:
at _GetBucketName (/base/data/home/apps/s~findit-for-me/waterfall-backend:13850-8d17315.407447171777310067/common/waterfall/buildbucket_client.py:35)
at is_swarmbucket_build (/base/data/home/apps/s~findit-for-me/waterfall-backend:13850-8d17315.407447171777310067/common/waterfall/buildbucket_client.py:102)
at AssignWarmCacheHost (/base/data/home/apps/s~findit-for-me/waterfall-backend:13850-8d17315.407447171777310067/services/swarmbot_util.py:181)
at TriggerTryJob (/base/data/home/apps/s~findit-for-me/waterfall-backend:13850-8d17315.407447171777310067/services/try_job.py:325)
at run (/base/data/home/apps/s~findit-for-me/waterfall-backend:13850-8d17315.407447171777310067/waterfall/flake/schedule_flake_try_job_pipeline.py:57)
at _run_internal (/base/data/home/apps/s~findit-for-me/waterfall-backend:13850-8d17315.407447171777310067/infra_api_clients/../third_party/pipeline/pipeline.py:1113)
at evaluate (/base/data/home/apps/s~findit-for-me/waterfall-backend:13850-8d17315.407447171777310067/infra_api_clients/../third_party/pipeline/pipeline.py:2158)

Context or examples:
https://pantheon.corp.google.com/errors/CPr2gcLw8IDdXA?time=P30D&filter&project=findit-for-me

Expected:

If try-job is triggered, master name should not be None.