Declaring a Property as constant raises an exception

import sys

from PySide2.QtCore import Property, QObject
# from PyQt5.QtCore import pyqtProperty as Property, QObject


class Foo(QObject):
    def __init__(self, parent=None):
        super().__init__(parent)
        self._foo_object = QObject()

    @Property(QObject, constant=True)
    def foo(self):
        return self._foo_object


if __name__ == "__main__":
    foo = Foo()

Traceback (most recent call last):
  File "/home/qt_user/main.py", line 7, in <module>
    class Foo(QObject):
  File "/home/qt_user/main.py", line 13, in Foo
    def foo(self):
TypeError: A constant property cannot have a WRITE method or a NOTIFY signal.

import sys

from PySide2.QtCore import Property, QObject


class Foo(QObject):
    def __init__(self, parent=None):
        super().__init__(parent)
        self._foo_object = QObject()

    def get_foo(self):
        return self._foo_object

    foo = Property(QObject, fget=get_foo, constant=True)


if __name__ == "__main__":
    foo = Foo()