class_docstr: ... purely for test coverage
docstr: LookupTable - Drivers - Null Driver - Id
docstr_tok: ["LookupTable","-","Drivers","-","Null","Driver","-","Id"]
code: def test_table_driver_id(self):
      """LookupTable - Drivers - Null Driver - Id"""
      assert_equal(self._driver.id, "null:1")
  
imports: from nose.tools import assert_equal, assert_raises, assert_true
  from streamalert.shared.lookup_tables.drivers import EphemeralDriver, NullDriver
  from streamalert.shared.lookup_tables.drivers_factory import construct_persistence_driver
  from streamalert.shared.lookup_tables.errors import LookupTablesConfigurationError
label_desc: Use image node_id 7 for calling the TestNullDriver obj's underlying member method code with example usage: obj.test_table_driver_id() without return types