[Designer] Card Payload Editor does not update when removing label/placeholder values from the Element Properties

Problem Description

Go to Designer

Steps to Reproduce:

1. Drag an Input.Text to the card area.
2. In the Element Properties toolbox, fill in the fields for Id, Label and Placeholder. Observe the Card Payload Editor updates with the correct key-value pair.
3. In the Element Properties toolbox, remove values for Label and Placeholder. Observe the Card Payload Editor does not update and does not remove the properties that have been cleared out.

Card JSON

{
    "$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
    "type": "AdaptiveCard",
    "version": "1.4",
    "body": [
        {
            "type": "TextBlock",
            "size": "Medium",
            "weight": "Bolder",
            "text": "Input.Text Elements",
            "horizontalAlignment": "Center",
            "wrap": true
        },
        {
            "type": "Input.Text",
            "label": "Name",
            "id": "SimpleVal",
            "placeholder": "Enter your name"
        },
        {
            "type": "Input.Text",
            "label": "Homepage",
            "style": "Url",
            "id": "UrlVal",
            "placeholder": "Enter your homepage url"
        },
        {
            "type": "Input.Text",
            "label": "Email",
            "style": "Email",
            "id": "EmailVal",
            "placeholder": "Enter your email"
        },
        {
            "type": "Input.Text",
            "label": "Phone",
            "style": "Tel",
            "id": "TelVal",
            "placeholder": "Enter your phone number"
        }
    ]
}

Screenshot

Start by reproducing the issue in the Adaptive Cards Designer using the steps provided, then trace how the Element Properties toolbox updates the Card Payload Editor. Done means clearing Label and Placeholder removes those properties from the generated card JSON.