code: def test_table_get_index_none(self):
      tbl = Table({"a": ["", "a", None, "b"], "b": [4, 3, 2, 1]})
      assert tbl.get_index() is None
  
imports: import sys
  from datetime import date, datetime
  from perspective.core.exception import PerspectiveError
  from perspective.table import Table
  from perspective.table._state import _PerspectiveStateManager
  from perspective.table.libpsppy import PerspectiveCppError, t_filter_op
  from pytest import raises
label_desc: Use image node_id 50 for calling the TestTable obj's underlying member method code with example usage: obj.test_table_get_index_none() without return types