createObject ignores null property assignment

import QtQuick
import QtQuick.Controls
import QtQuick.Layouts

ApplicationWindow {
    id: window
    width: 800
    height: 600
    visible: true

    Component.onCompleted: {
        // Works
//        let textArea = textAreaComponent.createObject(window.contentItem, { background: redRect })
        // No effect
        let textArea = textAreaComponent.createObject(window.contentItem, { background: null })
        title = textArea.background.toString()
    }

    Rectangle {
        id: redRect
        objectName: "redRect"
        color: 'red'
    }

    Component {
        id: textAreaComponent
        TextArea {
            text: "TextArea"
        }
    }
}