code: def test_empty_group_expr(self):
      grp = Group(0)
      prpty = Property(PropertyType(1))
  
      self.assertEqual(grp.get_best_expr(prpty), None)
      self.assertEqual(grp.get_best_expr_cost(prpty), None)
  
file_path: evadb/test/unit_tests/optimizer/test_group.py
imports: import unittest
  from mock import MagicMock
  from evadb.optimizer.group import Group
  from evadb.optimizer.group_expression import GroupExpression
  from evadb.optimizer.property import Property, PropertyType
label_desc: Use image node_id 4 for calling the TestGroup obj's underlying member method code with example usage: obj.test_empty_group_expr() without return types