cedricdeboom opened a new issue, #48005:
URL: https://github.com/apache/airflow/issues/48005
### Apache Airflow version
2.10.5
### If "Other Airflow 2 version" selected, which one?
_No response_
### What happened?
Upon expanding a task using a list of variables, the return value of the
task should be a list of all the individual return values. When the return
value of one mapped task is None, it is automatically filtered out of this
list. You might expect then that if _all_ mapped tasks return None, the list is
empty. However, that is not the case. Instead of returning an empty list, the
return value is None. This causes issues if the output is used to expand upon
in downstream tasks.
### What you think should happen instead?
The return value of an expanded task should _always_ be a list, even if all
the mapped tasks have returned None (in which case the list should be empty,
not None).
### How to reproduce
Example dag to reproduce.
```
import logging
from datetime import datetime
from airflow.decorators import dag, task
logger = logging.getLogger(__name__)
@dag(schedule=None, start_date=datetime(2024, 3, 20), catchup=False,
dag_id="example_dag")
def example_dag():
@task
def generate_data():
# Generating a list of numbers
return [1, 3]
@task
def filter_data(number):
# Filtering only even numbers
return number if number % 2 == 0 else None
@task
def display_results(results):
logger.info(results)
numbers = generate_data()
filtered_numbers = filter_data.expand(number=numbers)
display_results(filtered_numbers)
example_dag()
```
### Operating System
MacOS Sequoia 15.3.2
### Versions of Apache Airflow Providers
_No response_
### Deployment
Virtualenv installation
### Deployment details
Standalone
### Anything else?
_No response_
### Are you willing to submit PR?
- [ ] Yes I am willing to submit a PR!
### Code of Conduct
- [x] I agree to follow this project's [Code of
Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)
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