PyQt 5.5 roleNames error

Application.qml

import QtQuick 2.4

Item {
    width: 400
    height: 600

    ListView {
        anchors.fill: parent
        model: _BE.model
        delegate: Text { text: hello }
    }
}

run_me.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

# works correctly with SIP 4.16.6-snapshot-bf261aa4b322 and PyQt 5.4.1
# causes the following error when run with SIP 4.16.9-snapshot-8dd533ab6ce9 and
# PyQt 5.5-snapshot-6fd628724de4:
#
#    TypeError: invalid result type from DummyModel.roleNames()
#
# tried on Python 3.4 only

import os
import sys
import sip
import signal
from PyQt5.QtGui import QGuiApplication
from PyQt5 import QtCore
from PyQt5.QtCore import QUrl, Qt, QVariant, pyqtSlot, QAbstractListModel
from PyQt5.QtQuick import QQuickView


class DummyModel(QAbstractListModel):
    ROLES = ("hello",)
    _ROLE_MAP = {}

    def _setup_roles(self):
        keys = range(Qt.UserRole + 1, Qt.UserRole + 1 + len(self.ROLES))
        self._ROLE_MAP = dict(zip(keys, self.ROLES))

    def roleNames(self):
        return self._ROLE_MAP

    def __init__(self, model_size, parent=None):
        QAbstractListModel.__init__(self, parent)
        self._setup_roles()
        self.model_size = model_size

    def data(self, qindex, role):
        if not qindex.isValid():
            print("Invalid index, returning empty QVariant")
            return QVariant()
        if role not in self._ROLE_MAP:
            print("Invalid role, returning empty QVariant")
            return QVariant()

        return "Item #{}".format(qindex.row())

    @pyqtSlot(result=int)
    def rowCount(self, parent):
        if parent.isValid():
            print("This shouldn't happen")
        return self.model_size


def run():
    signal.signal(signal.SIGINT, signal.SIG_DFL)

    print("SIP version: {}".format(sip.SIP_VERSION_STR))
    print("PyQt version: {}".format(QtCore.PYQT_VERSION_STR))

    app = QGuiApplication(sys.argv)
    qml_url = QUrl.fromLocalFile(os.path.join('Application.qml'))
    gui_entrypoint = { 'model': DummyModel(80) }
    view = QQuickView()
    view.rootContext().setContextProperty('_BE', gui_entrypoint)
    view.setSource(qml_url)

    view.show()
    sys.exit(app.exec_())


if __name__ == '__main__':
    run()