code: def test_map_can_only_return_none_if_missing_value_is_none(self):
      # Should work.
      la = LabelArray(self.strs, missing_value=None)
      result = la.map(lambda x: None)
  
      check_arrays(
          result,
          LabelArray(np.full_like(self.strs, None), missing_value=None),
      )
  
      la = LabelArray(self.strs, missing_value="__MISSING__")
      with self.assertRaises(TypeError):
          la.map(lambda x: None)
  
imports: from itertools import product
  from operator import eq, ne
  import warnings
  import numpy
  from toolz import take
  from zipline.lib.labelarray import LabelArray
  from zipline.testing import check_arrays, parameter_space, ZiplineTestCase
  from zipline.testing.predicates import assert_equal
  from zipline.utils.compat import unicode
label_desc: Use image node_id 7 for calling the LabelArrayTestCase obj's underlying member method code with example usage: obj.test_map_can_only_return_none_if_missing_value_is_none() without return types