ParamSpec(bound=None) incorrectly sets __bound__ to NoneType

Bug report

Bug description:

When creating a ParamSpec with bound=None, the runtime bound attribute is set to <class 'NoneType'> instead of None.

How to reproduce

from typing import ParamSpec, Callable

P1 = ParamSpec("P")
P2 = ParamSpec("P", bound=None)
P3 = ParamSpec("P", bound=Callable[[int, str], float])

def check_bound(label, p, expected):
    got = p.__bound__
    ok = (got is expected)
    exp_s = repr(expected)
    got_s = repr(got)
    print(f"{label}.__bound__ should be {exp_s}, got {got_s}  ->  {'OK' if ok else 'FAIL'}")

check_bound("P1", P1, None)
check_bound("P2", P2, None)
check_bound("P3", P3, Callable[[int, str], float])

Current behavior

d:\MyCode\cpython\PCbuild\amd64>python_d.exe py_bound.py
P1.__bound__ should be None, got <class 'NoneType'>  ->  FAIL
P2.__bound__ should be None, got <class 'NoneType'>  ->  FAIL
P3.__bound__ should be typing.Callable[[int, str], float], got typing.Callable[[int, str], float]  ->  OK

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-142751

从 ParamSpec 的实现开始，并在 CPython main 上运行提供的复现代码。验证未绑定的 ParamSpec 和使用 bound=None 创建的 ParamSpec 将 bound 暴露为 None，而显式绑定的 ParamSpec 会保留其 bound；该 issue 链接到了 PR gh-142751，因此请先查看这项工作。