code: def test_null(self):
      self.assertEqual(parse("null", self.sym), ct.DataShape(ct.null))
  
imports: from __future__ import absolute_import, division, print_function
  import unittest
  import pytest
  from datashader import datashape
  from datashader.datashape.util.testing import assert_dshape_equal
  from datashader.datashape.parser import parse
  from datashader.datashape import coretypes
  from datashader.datashape import DataShapeSyntaxError
label_desc: Use image node_id 6 for calling the TestDataShapeParseBasicDType obj's underlying member method code with example usage: obj.test_null() without return types