Python 3.10 compiler adds None to co_consts even when None is not used at all.

```
$ cat x1.py
def foo():
    "docstring"
    return 42

import dis
dis.dis(foo)
print(foo.__code__.co_consts)

$ python3.9 x1.py
  3           0 LOAD_CONST               1 (42)
              2 RETURN_VALUE
('docstring', 42)

$ python3.10 x1.py
  3           0 LOAD_CONST               1 (42)
              2 RETURN_VALUE
('docstring', 42, None)
```