diff --git a/bugbear.py b/bugbear.py
index 06e598d..e47ede1 100644
--- a/bugbear.py
+++ b/bugbear.py
@@ -155,12 +155,13 @@ class BugBearChecker:
             return True
 
         for i in range(2, len(code) + 1):
-            if code[:i] in self.options.select:
+            if self.options.select and code[:i] in self.options.select:
                 return True
 
             # flake8 >=4.0: Also check for codes in extend_select
             if (
                 hasattr(self.options, "extend_select")
+                and self.options.extend_select
                 and code[:i] in self.options.extend_select
             ):
                 return True

diff --git a/tests/test_bugbear.py b/tests/test_bugbear.py
index a974cf4..12469e6 100644
--- a/tests/test_bugbear.py
+++ b/tests/test_bugbear.py
@@ -438,6 +438,16 @@ class BugbearTestCase(unittest.TestCase):
             ),
         )
 
+    def test_b9_flake8_next_default_options(self):
+        filename = Path(__file__).absolute().parent / "b950.py"
+
+        # in flake8 next, unset select / extend_select will be `None` to
+        # signify the default values
+        mock_options = Namespace(select=None, extend_select=None)
+        bbc = BugBearChecker(filename=str(filename), options=mock_options)
+        errors = list(bbc.run())
+        self.assertEqual(errors, [])
+
     def test_selfclean_bugbear(self):
         filename = Path(__file__).absolute().parent.parent / "bugbear.py"
         proc = subprocess.run(

`should_warn` is incompatible with flake8 (next)
minimal reproduction (trigger any `B9*` warning with the default settings)

```console
$ rm -rf venv && virtualenv -qq venv && venv/bin/pip install -qq git+https://github.com/pycqa/flake8 git+https://github.com/pycqa/flake8-bugbear && venv/bin/flake8 --config /dev/null - <<< $'class C:\n    def __init__(wat): ...'
Traceback (most recent call last):
  File "venv/bin/flake8", line 8, in <module>
    sys.exit(main())
  File "/tmp/y/venv/lib/python3.8/site-packages/flake8/main/cli.py", line 22, in main
    app.run(argv)
  File "/tmp/y/venv/lib/python3.8/site-packages/flake8/main/application.py", line 336, in run
    self._run(argv)
  File "/tmp/y/venv/lib/python3.8/site-packages/flake8/main/application.py", line 325, in _run
    self.run_checks()
  File "/tmp/y/venv/lib/python3.8/site-packages/flake8/main/application.py", line 229, in run_checks
    self.file_checker_manager.run()
  File "/tmp/y/venv/lib/python3.8/site-packages/flake8/checker.py", line 252, in run
    self.run_serial()
  File "/tmp/y/venv/lib/python3.8/site-packages/flake8/checker.py", line 237, in run_serial
    checker.run_checks()
  File "/tmp/y/venv/lib/python3.8/site-packages/flake8/checker.py", line 531, in run_checks
    self.run_ast_checks()
  File "/tmp/y/venv/lib/python3.8/site-packages/flake8/checker.py", line 435, in run_ast_checks
    for (line_number, offset, text, _) in runner:
  File "/tmp/y/venv/lib/python3.8/site-packages/bugbear.py", line 61, in run
    if self.should_warn(e.message[:4]):
  File "/tmp/y/venv/lib/python3.8/site-packages/bugbear.py", line 158, in should_warn
    if code[:i] in self.options.select:
TypeError: argument of type 'NoneType' is not iterable
```

looking at the code, you should be able to delete `should_warn` entirely and rely on `extend-select` (and delete `load_file` while you're at it!)
tests/test_bugbear.py::BugbearTestCase::test_b9_flake8_next_default_options
tests/test_bugbear.py::BugbearTestCase::test_b001 tests/test_bugbear.py::BugbearTestCase::test_b002 tests/test_bugbear.py::BugbearTestCase::test_b003 tests/test_bugbear.py::BugbearTestCase::test_b004 tests/test_bugbear.py::BugbearTestCase::test_b005 tests/test_bugbear.py::BugbearTestCase::test_b006_b008 tests/test_bugbear.py::BugbearTestCase::test_b007 tests/test_bugbear.py::BugbearTestCase::test_b008_extended tests/test_bugbear.py::BugbearTestCase::test_b009_b010 tests/test_bugbear.py::BugbearTestCase::test_b011 tests/test_bugbear.py::BugbearTestCase::test_b012 tests/test_bugbear.py::BugbearTestCase::test_b013 tests/test_bugbear.py::BugbearTestCase::test_b014 tests/test_bugbear.py::BugbearTestCase::test_b015 tests/test_bugbear.py::BugbearTestCase::test_b016 tests/test_bugbear.py::BugbearTestCase::test_b017 tests/test_bugbear.py::BugbearTestCase::test_b018_classes tests/test_bugbear.py::BugbearTestCase::test_b018_functions tests/test_bugbear.py::BugbearTestCase::test_b019 tests/test_bugbear.py::BugbearTestCase::test_b020 tests/test_bugbear.py::BugbearTestCase::test_b021_classes tests/test_bugbear.py::BugbearTestCase::test_b022 tests/test_bugbear.py::BugbearTestCase::test_b901 tests/test_bugbear.py::BugbearTestCase::test_b902 tests/test_bugbear.py::BugbearTestCase::test_b902_py38 tests/test_bugbear.py::BugbearTestCase::test_b903 tests/test_bugbear.py::BugbearTestCase::test_b904 tests/test_bugbear.py::BugbearTestCase::test_b950 tests/test_bugbear.py::BugbearTestCase::test_b9_extend_select tests/test_bugbear.py::BugbearTestCase::test_b9_select tests/test_bugbear.py::BugbearTestCase::test_selfclean_test_bugbear tests/test_bugbear.py::TestFuzz::test_does_not_crash_on_any_valid_code tests/test_bugbear.py::TestFuzz::test_does_not_crash_on_call_in_except_statement tests/test_bugbear.py::TestFuzz::test_does_not_crash_on_site_code tests/test_bugbear.py::TestFuzz::test_does_not_crash_on_tuple_expansion_in_except_statement