TypeError: Parameter list cannot be empty for TypeVarTuple

There is a problem with typing_extensions that doesn't happen with typing. Running the program with python3.11 works, but with python3.10 with typing_extensions throws:

Traceback (most recent call last):
  File ".../main.py", line 48, in <module>
    main()
  File ".../main.py", line 40, in main
    signal: Signal[()] = Signal[()]()
  File "/usr/lib/python3.10/typing.py", line 312, in inner
    return func(*args, **kwds)
  File "/usr/lib/python3.10/typing.py", line 1328, in __class_getitem__
    raise TypeError(
TypeError: Parameter list to Signal[...] cannot be empty

from __future__ import annotations

from typing_extensions import Callable, TypeVarTuple, Generic, Unpack, List, TypeVar

VarArgs = TypeVarTuple('VarArgs')


class Signal(Generic[Unpack[VarArgs]]):

    def __init__(self):
        self.functions: List[Callable[..., None]] = []
        """
        Simple mechanism that allows abstracted invocation of callbacks. Multiple callbacks can be attached to a signal
        so that they are all called when the signal is emitted.
        """

    def connect(self, function: Callable[..., None]):
        """
        Add a callback to this Signal
        :param function: callback to call when emited
        """
        self.functions.append(function)

    def emit(self, *args: Unpack[VarArgs]):
        """
        Call all callbacks with the arguments passed
        :param args: arguments for the signal, must be the same type as type parameter
        """
        for function in self.functions:
            if args:
                function(*args)
            else:
                function()


def main():
    def signalEmptyCall():
        print("Hello!")

    signal: Signal[()] = Signal[()]()

    signal.connect(signalEmptyCall)

    signal.emit()


if __name__ == '__main__':
    main()

从 main.py 中的复现开始，比较 Python 3.10 使用 typing_extensions 与 Python 3.11 使用 typing 时 Signal[()] 的行为。跟踪 TypeVarTuple 和空参数的处理，然后添加或更新一个回归测试，证明空参数列表能够被一致地接受。