xcom_pull doesn't allow passing key=None or not specifying key in Airflow 3

### Apache Airflow version 3.0.1 ### If "Other Airflow 2 version" selected, which one? _No response_ ### What happened? xcoms = context['ti'].xcom_pull( run_id=run_id, task_ids=task_ids, key=None, ) the above code will report error said key cannot be None: `Key` `Input should be a valid string [type=string_type, input_value=None, input_type=NoneType]` however in Airflow 2 with the above code I can get all xcoms of these tasks in this dag run ### What you think should happen instead? I expect to get all xcoms of these tasks in this dag run, means if key=None, it should return all xcoms regardless of their xcom key, the sql statement may be like: ``` SELECT * from xcom WHERE run_id=run_id and task_ids in [...] ``` no filter on xcom key In Airflow 2 this works. ### How to reproduce xcoms = context['ti'].xcom_pull( run_id=run_id, task_ids=task_ids, key=None, ) ### Operating System ubuntu ### Versions of Apache Airflow Providers _No response_ ### Deployment Official Apache Airflow Helm Chart ### Deployment details _No response_ ### Anything else? _No response_ ### Are you willing to submit PR? - [x] 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)