
**Apache Airflow version**:

master

**What happened**:

https://github.com/apache/airflow/blob/master/airflow/models/baseoperator.py#L356 --> should be timedelta not datetime


tests/serialization/test_dag_serialization.py
"""
        Test that params work both on Serialized DAGs & Tasks
        """
        dag = DAG(dag_id='simple_dag')
        BaseOperator(task_id='simple_task', dag=dag, params=val, start_date=datetime(2019, 8, 1))
        serialized_dag = SerializedDAG.to_dict(dag)
        if val:
            assert "params" in serialized_dag["dag"]["tasks"][0]
        else:
            assert "params" not in serialized_dag["dag"]["tasks"][0]
        deserialized_dag = SerializedDAG.from_dict(serialized_dag)
        deserialized_simple_task = deserialized_dag.task_dict["simple_task"]
        assert expected_val == deserialized_simple_task.params
    def test_extra_serialized_field_and_operator_links(self):
        """
        Assert extra field exists & OperatorLinks defined in Plugins and inbuilt Operator Links.
        This tests also depends on GoogleLink() registered as a plugin
        in tests/plugins/test_plugin.py
        The function tests that if extra operator links are registered in plugin
        in ``operator_extra_links`` and the same is also defined in
        the Operator in ``BaseOperator.operator_extra_links``, it has the correct
        extra link.
        """
        test_date = datetime(2019, 8, 1)