Metrics reporting failed bigtable io

Details see comment in https://github.com/apache/beam/pull/15562.

We are seeing errors which possibly originate from this code:def write_mutate_metrics(self, rows): for status in rows: grpc_status_string = ( ServiceCallMetric.bigtable_error_code_to_grpc_status_string( status.code)) self.service_call_metric.call(grpc_status_string)Error message:
File "/usr/local/lib/python3.6/site-packages/apache_beam/io/gcp/bigtableio.py", line 123, in write_mutate_metrics status.code)) AttributeError: 'NoneType' object has no attribute 'code' [while running 'Write event Bigtable row/ParDo(_BigTableWriteFn)-ptransform-58134']Would you have any idea about this issue?We are runningPython 3.6
Beam 2.35
GCP DataflowRunner
In addition, the choice of parameter name (rows) is confusing. Perhaps something like responses or response_list ?
https://cloud.google.com/bigtable/docs/writing-data#batch
https://googleapis.dev/python/bigtable/1.3.0/_modules/google/cloud/bigtable/table.html#Table.mutate_rows