PostgresToGCSOperator fail on empty table and use_server_side_cursor=True

[PikaYellow35]

Apache Airflow Provider(s)

google

Versions of Apache Airflow Providers

apache-airflow-providers-google==6.1.0

Apache Airflow version

2.2.2 (latest released)

Operating System

Debian GNU/Linux 10 (buster)

Deployment

Other Docker-based deployment

Deployment details

No response

What happened

When I'm execute PostgresToGCSOperator on empty table and set use_server_side_cursor=True the operator fails with error:

Traceback (most recent call last):
  File "/home/airflow/.local/lib/python3.9/site-packages/airflow/models/taskinstance.py", line 1332, in _run_raw_task
    self._execute_task_with_callbacks(context)
  File "/home/airflow/.local/lib/python3.9/site-packages/airflow/models/taskinstance.py", line 1458, in _execute_task_with_callbacks
    result = self._execute_task(context, self.task)
  File "/home/airflow/.local/lib/python3.9/site-packages/airflow/models/taskinstance.py", line 1514, in _execute_task
    result = execute_callable(context=context)
  File "/home/airflow/.local/lib/python3.9/site-packages/airflow/providers/google/cloud/transfers/sql_to_gcs.py", line 154, in execute
    files_to_upload = self._write_local_data_files(cursor)
  File "/home/airflow/.local/lib/python3.9/site-packages/airflow/providers/google/cloud/transfers/sql_to_gcs.py", line 213, in _write_local_data_files
    row = self.convert_types(schema, col_type_dict, row)
  File "/home/airflow/.local/lib/python3.9/site-packages/airflow/providers/google/cloud/transfers/sql_to_gcs.py", line 174, in convert_types
    return [self.convert_type(value, col_type_dict.get(name)) for name, value in zip(schema, row)]
TypeError: 'NoneType' object is not iterable

Operator command when I'm using:

task_send = PostgresToGCSOperator(
            task_id=f'send_{table}',
            postgres_conn_id='postgres_raw',
            gcp_conn_id=gcp_conn_id,
            sql=f'SELECT * FROM public.{table}',
            use_server_side_cursor=True,
            bucket=bucket,
            filename=f'{table}.csv',
            export_format='csv',
        )

What you expected to happen

I'm expected, that operator on empty table not creating file and no upload it on Google Cloud.

How to reproduce

• Create empty postgresql table.
• Create dag with task with PostgresToGCSOperator. that upload this table in Google Cloud.

Anything else

No response

Are you willing to submit PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[boring-cyborg]

Thanks for opening your first issue here! Be sure to follow the issue template!

[potiuk]

Maybe you would like to contribute a PR to fix it @PikaYellow35 - we have > 1800 contributors, you can become one of them :)

[rsg17]

Hi @potiuk - I am new to Airflow and would like to try and take a pass at this.

I have breeze setup; have created one PR; but nothing on the operators side. I will go through the corresponding code and contributing page again. Do let me know if you have any pointers..

[eladkal]

@rsg17 feel free to join Airflow slack. There are channels for support like: airflow-how-to-pr