Preoptimize causes error with environment setup

Setting \--experiments=pre_optimize=all causes an error with StatisticsGen in the TFX taxi example pipeline [1]:

File "[redacted]/apache_beam/runners/portability/fn_api_runner_transforms.py", line 250, in executable_stage_transform
environment=components.environments[self.environment],
TypeError: None has type NoneType, but expected one of: bytes, unicode [while running 'Run[StatisticsGen]']

cc [~angoenka]

[1] https://github.com/tensorflow/tfx/blob/ff314a6803675548c89a016a5110a91e5bf98024/tfx/examples/chicago_taxi_pipeline/taxi_pipeline_portable_beam.py#L155

Imported from Jira [BEAM-9445](https://issues.apache.org/jira/browse/BEAM-9445). Original Jira may contain additional context.
Reported by: ibzib.