"Cannot assign object to list property"

[CrouchEndTiger]

Hi!

I'm having some trouble assigning a T.Popup root-type to the .children property of another type. I get the error message: "Cannot assign object to list property" Couldn't find any references to the same problem.

I've got a PresentationPanel type, which should be able to display an arbitrary component for a kind-of "sticker app". It works fine on most types, but it has trouble with my custom ContextMenu type with a base-type of T.Popup.

Any help would be massively appreciated!

main.qml:

import QtQuick 2.12
import QtQuick.Window 2.12

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Popup Bug!")
    color: "#313A68"

    DisplayPanel
    {
        x: 100
        y: 100

        title: "Context Menu"
        content: MyContextMenu
        {
            visible: true
        }
    }
}

DisplayPanel.qml:

Rectangle
{
    radius: 20
    color: "#5AA1BF"

    default property alias content: mainPanel.children

    implicitWidth: Math.max(
                       titleComponent.width + 2 * priv.padding,
                       mainPanel.width + 2 * priv.padding)

    implicitHeight: titleComponent.height + mainPanel.height + 3 * priv.padding

    property alias title: titleComponent.text

    QtObject
    {
        id: priv
        readonly property real padding: 10
    }

    Text
    {
        id: titleComponent
        anchors
        {
            top: parent.top
            left: parent.left
            margins: priv.padding
        }
    }

    ColumnLayout
    {
        id: mainPanel
        anchors
        {
            top: titleComponent.bottom
            left: parent.left
            margins: priv.padding
        }
    }
}

MyContextMenu.qml

import QtQuick 2.0
import QtQuick.Templates 2.12 as T

T.Popup
{
    id:root

    implicitWidth: mainView.width
    implicitHeight: mainView.height

    margins: 0

    function popup(mouseX, mouseY)
    {
        x = mouseX
        y = mouseY
        root.open()
    }

    contentItem: ListView
    {
        id: mainView
        model: listModel

        width: 100
        height: model.count * 20

        delegate: Text
        {
            height: 20
            text: model.text
        }
    }

    background: Rectangle
    {
        id: background
        anchors.fill: parent
        color: "#DF69AB"
    }

    ListModel
    {
        id: listModel
        ListElement{ text: "Item 1" }
        ListElement{ text: "Item 2" }
        ListElement{ text: "Item 3" }
        ListElement{ text: "Item 4" }
    }
}