### Body

Currently `start_date` is mandatory parameter.
For DAGs with `schedule=None` we can relax this requirement as no scheduling calculation needed so the `start_date` parameter isn't used.

### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.
"""Get the Default DAG View, returns the default config value if DagModel does not have a value."""
        
        return self.default_view or airflow_conf.get_mandatory_value("webserver", "dag_default_view").lower()
    @property
    def safe_dag_id(self):
        return self.dag_id.replace(".", "__dot__")
    @property
    def relative_fileloc(self) -> pathlib.Path | None:
        """File location of the importable dag 'file' relative to the configured DAGs folder."""
        if self.fileloc is None:
            return None
        path = pathlib.Path(self.fileloc)
        try:
            return path.relative_to(settings.DAGS_FOLDER)
        except ValueError:
            
            return path
    @provide_session
    def set_is_paused(self, is_paused: bool, including_subdags: bool = True, session=NEW_SESSION) -> None: