https://airflow.apache.org/docs/apache-airflow/stable/configurations-ref.html#store-dag-code

![Captura de pantalla 2021-05-26 a las 17 47 56](https://user-images.githubusercontent.com/11339132/119691160-a2049a00-be4a-11eb-8f55-0ad2c6117620.png)

The Default is True or None?
tests/core/test_configuration.py
assert conf.has_option("core", "FERNET_KEY")
        assert not conf.has_option("core", "FERNET_KEY_CMD")
        fernet_key = conf.get('core', 'FERNET_KEY')
        with conf_vars({('core', 'FERNET_KEY_CMD'): 'printf HELLO'}):
            fallback_fernet_key = conf.get("core", "FERNET_KEY")
        assert fernet_key == fallback_fernet_key
    def test_config_throw_error_when_original_and_fallback_is_absent(self):
        assert conf.has_option("core", "FERNET_KEY")
        assert not conf.has_option("core", "FERNET_KEY_CMD")
        with conf_vars({('core', 'fernet_key'): None}):
            with pytest.raises(AirflowConfigException) as ctx:
                conf.get("core", "FERNET_KEY")
        exception = str(ctx.value)
        message = "section/key [core/fernet_key] not found in config"
        assert message == exception
    def test_config_override_original_when_non_empty_envvar_is_provided(self):
        key = "AIRFLOW__CORE__FERNET_KEY"
        value = "some value"
        with mock.patch.dict('os.environ', {key: value}):
            fernet_key = conf.get('core', 'FERNET_KEY')
        assert value == fernet_key
    def test_config_override_original_when_empty_envvar_is_provided(self):
        key = "AIRFLOW__CORE__FERNET_KEY"
        value = "some value"
        with mock.patch.dict('os.environ', {key: value}):
            fernet_key = conf.get('core', 'FERNET_KEY')
        assert value == fernet_key
    @mock.patch.dict("os.environ", {"AIRFLOW__CORE__DAGS_FOLDER": "/tmp/test_folder"})
    def test_write_should_respect_env_variable(self):