class_docstr: Test the MWSL1BFile reader.
docstr: Test get dataset return none if data does not exist.
docstr_tok: ["Test","get","dataset","return","none","if","data","does","not","exist","."]
code: def test_get_dataset_return_none_if_data_not_exist(self, reader):
      """Test get dataset return none if data does not exist."""
      dataset_id = {"name": "unknown"}
      dataset_info = {"file_key": "non/existing/data"}
      dataset = reader.get_dataset(dataset_id, dataset_info)
      assert dataset is None
  
imports: import logging
  from datetime import datetime
  from unittest.mock import patch
  import numpy
  import pytest
  import xarray
  from netCDF4 import Dataset
  from satpy.readers.mws_l1b import MWSL1BFile, get_channel_index_from_name
label_desc: Use image node_id 11 for calling the TestMwsL1bNCFileHandler obj's underlying member method code with example usage: obj.test_get_dataset_return_none_if_data_not_exist(reader) without return types