### 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.
return f"<DAG: {self.dag_id}>"
    def __eq__(self, other):
        if type(self) == type(other):
            
            
            return all(getattr(self, c, None) == getattr(other, c, None) for c in self._comps)
        return False
    def __ne__(self, other):
        return not self == other
    def __lt__(self, other):
        return self.dag_id < other.dag_id
    def __hash__(self):
        hash_components = [type(self)]
        for c in self._comps:
            
            if c == "task_ids":
                val = tuple(self.task_dict)
            else:
                val = getattr(self, c, None)
            try:
                hash(val)
                hash_components.append(val)
            except TypeError:
                hash_components.append(repr(val))
        return hash(tuple(hash_components))
    
    def __enter__(self):
        DagContext.push_context_managed_dag(self)
        return self
    def __exit__(self, _type, _value, _tb):