code: def test_null_values(self):
      t = Text(null_values=["Bad Value"])
      self.assertEqual(t.cast("Bad Value"), None)
  
imports: import datetime
  import pickle
  import unittest
  from decimal import Decimal
  import parsedatetime
  from agate.data_types import Boolean, Date, DateTime, Number, Text, TimeDelta
  from agate.exceptions import CastError
label_desc: Use image node_id 5 for calling the TestText obj's underlying member method code with example usage: obj.test_null_values() without return types