unset property overwrites text node

text node overwrite example.txt

[
    {
        "id": "95b5b1dca3a6b5f6",
        "type": "inject",
        "z": "e4fd59d6388ce474",
        "name": "both",
        "props": [
            {
                "p": "payload"
            },
            {
                "p": "topic",
                "vt": "str"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "both",
        "payload": "",
        "payloadType": "date",
        "x": 290,
        "y": 280,
        "wires": [
            [
                "935c46bee3d83810"
            ]
        ]
    },
    {
        "id": "935c46bee3d83810",
        "type": "function",
        "z": "e4fd59d6388ce474",
        "name": "Set Two Properties",
        "func": "var myMsg = {};\nmyMsg.payload = {};\nmyMsg.topic = msg.topic;\n\nif ((msg.topic == \"both\") || (msg.topic == \"first\")) {\n    myMsg.payload.first = msg.payload;\n}\n\nif ((msg.topic == \"both\") || (msg.topic == \"second\")) {\n    myMsg.payload.second = msg.payload;\n}\n\nreturn myMsg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 490,
        "y": 220,
        "wires": [
            [
                "4cbe53432e434550",
                "2d873a5f37ee7060",
                "e3d03199a3da2725"
            ]
        ]
    },
    {
        "id": "4cbe53432e434550",
        "type": "debug",
        "z": "e4fd59d6388ce474",
        "name": "debug 2",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "payload",
        "targetType": "msg",
        "statusVal": "",
        "statusType": "auto",
        "x": 720,
        "y": 280,
        "wires": []
    },
    {
        "id": "9f225f850a0f5355",
        "type": "inject",
        "z": "e4fd59d6388ce474",
        "name": "first",
        "props": [
            {
                "p": "payload"
            },
            {
                "p": "topic",
                "vt": "str"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "first",
        "payload": "",
        "payloadType": "date",
        "x": 290,
        "y": 180,
        "wires": [
            [
                "935c46bee3d83810"
            ]
        ]
    },
    {
        "id": "c243adf09777690e",
        "type": "inject",
        "z": "e4fd59d6388ce474",
        "name": "second",
        "props": [
            {
                "p": "payload"
            },
            {
                "p": "topic",
                "vt": "str"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "second",
        "payload": "",
        "payloadType": "date",
        "x": 290,
        "y": 220,
        "wires": [
            [
                "935c46bee3d83810"
            ]
        ]
    },
    {
        "id": "2d873a5f37ee7060",
        "type": "ui_text",
        "z": "e4fd59d6388ce474",
        "group": "b7d12b8d.651c8",
        "order": 1,
        "width": 0,
        "height": 0,
        "name": "first",
        "label": "first",
        "format": "{{msg.payload.first}}",
        "layout": "row-spread",
        "className": "",
        "x": 710,
        "y": 180,
        "wires": []
    },
    {
        "id": "e3d03199a3da2725",
        "type": "ui_text",
        "z": "e4fd59d6388ce474",
        "group": "b7d12b8d.651c8",
        "order": 1,
        "width": 0,
        "height": 0,
        "name": "second",
        "label": "second",
        "format": "{{msg.payload.second}}",
        "layout": "row-spread",
        "className": "",
        "x": 720,
        "y": 220,
        "wires": []
    },
    {
        "id": "b7d12b8d.651c8",
        "type": "ui_group",
        "name": "Default",
        "tab": "fe5d396a.0d6d4",
        "order": 1,
        "disp": true,
        "width": "20",
        "collapse": false
    },
    {
        "id": "fe5d396a.0d6d4",
        "type": "ui_tab",
        "name": "Home",
        "icon": "dashboard",
        "disabled": false,
        "hidden": false
    }
]