Error in the execution of an overload signal

import sys

from PySide2.QtCore import (
    QCoreApplication,
    QRunnable,
    QObject,
    QThread,
    QThreadPool,
    Slot,
    Signal,
)

class WorkerSignals(QObject):
    test_sig = Signal((), (str,), (int,))
    finished = Signal()


# Test worker
class Worker(QRunnable):
    def __init__(self):
        super().__init__()
        self.signals = WorkerSignals()

    def run(self):
        print("1. send")
        self.signals.test_sig.emit()
        QThread.sleep(1)
        print("2. send")
        self.signals.test_sig[int].emit(100000)
        QThread.sleep(1)
        print("3. send")
        self.signals.test_sig.emit()
        QThread.sleep(1)
        print("4. send")
        self.signals.test_sig[str].emit("a")
        QThread.sleep(1)
        print("5. send")
        self.signals.test_sig.emit()
        QThread.sleep(1)
        print("6. send")
        self.signals.test_sig[str].emit(10000)
        QThread.sleep(1)
        print("7. send")
        self.signals.test_sig.emit()
        QThread.sleep(1)
        self.signals.finished.emit()


class Receiver(QObject):
    def __init__(self):
        super().__init__()
        self.threadpool = QThreadPool()

    def run_test(self):
        worker = Worker()
        worker.signals.test_sig.connect(self.test_func)
        worker.signals.test_sig[int].connect(self.test_func)
        worker.signals.test_sig[str].connect(self.test_func)
        worker.signals.finished.connect(QCoreApplication.quit)
        self.threadpool.start(worker)

    @Slot()
    @Slot(int)
    @Slot(str)
    def test_func(self, arg=None):
        print("receive:", arg, type(arg))


if __name__ == "__main__":
    app = QCoreApplication(sys.argv)
    receiver = Receiver()
    receiver.run_test()
    sys.exit(app.exec_())

1. send
2. send
receive: 100000 <class 'int'>
3. send
4. send
receive: a <class 'str'>
receive: a <class 'str'>
5. send
6. send
receive: 10000 <class 'int'>
7. send

1. send
receive: None <class 'NoneType'>
2. send
receive: 100000 <class 'int'>
3. send
receive: None <class 'NoneType'>
4. send
receive: a <class 'str'>
5. send
receive: None <class 'NoneType'>
6. send
receive: 10000 <class 'int'>
7. send
receive: None <class 'NoneType'>