
**Apache Airflow version**:
2.0.0

**Environment**:

- **OS** (e.g. from /etc/os-release): Ubuntu 20.04 LTS
- **Python version**: 3.8
- **Kernel** (e.g. `uname -a`): x86_64 x86_64 x86_64 GNU/Linux 5.4.0-58-generic #64-Ubuntu
- **Install tools**: pip


**What happened**:

Airflow 2.0 does not send metrics to statsD.

I configure Airflow with official documentation (https://airflow.apache.org/docs/apache-airflow/stable/logging-monitoring/metrics.html) and by this article https://dstan.medium.com/run-airflow-statsd-grafana-locally-16b372c86524 (but I used port 8125). 

I turned on statsD:

```ini
statsd_on = True
statsd_host = localhost
statsd_port = 8125
statsd_prefix = airflow
```

But I do not see airflow metrics at http://localhost:9102/metrics (statsD metrics endpoint).

---

P.S. I noticed this error just using Airflow 2.0. In version 1.10.13 everything is ok in the same environment.

Thank you for advance.



airflow/stats.py
"""A function that validate the statsd stat name, apply changes to the stat name
    if necessary and return the transformed stat name.
    """
    if not isinstance(stat_name, str):
        raise InvalidStatsNameException('The stat_name has to be a string')
    if len(stat_name) > max_length:
        raise InvalidStatsNameException(
            textwrap.dedent(
                """\
            The stat_name ({stat_name}) has to be less than {max_length} characters.
        """.format(
                    stat_name=stat_name, max_length=max_length
                )
            )
        )
    if not all((c in ALLOWED_CHARACTERS) for c in stat_name):
        raise InvalidStatsNameException(
            textwrap.dedent(
                """\
            The stat name ({stat_name}) has to be composed with characters in
            {allowed_characters}.
            """.format(
                    stat_name=stat_name, allowed_characters=ALLOWED_CHARACTERS
                )
            )
        )
    return stat_name
def get_current_handler_stat_name_func() -> Callable[[str], str]: