Jsonata editor test error with transform function (3.1.3)

Current Behavior

I have just updated a node-red server to 3.1.3 and have notice a bug in the JSONata test enviroment in the change node editor.

Prior to update 3.1 this used to work fine.

If you set an array of objects in payload in the test window

{
    "payload": [
        {
            "w1": "This",
            "w2": "is",
            "w3": "Big!"
        },
        {
            "w1": "Big",
            "w2": "as",
            "w3": "this?"
        }
    ]
}

Then use this expression containing the transform function

$$.payload ~> |$|
 {"a":"a"}
|

An error is reported

Error evaluating expression:
  Cannot set properties of null (setting 'a')

The expression will run just fine and produce an
output

{
    "_msgid": "b5e1ea5de4e4373f",
    "payload": [
        {
            "w1": "This",
            "w2": "is",
            "w3": "Big!",
            "a": "a"
        },
        {
            "w1": "Big",
            "w2": "as",
            "w3": "this?",
            "a": "a"
        }
    ],
    "topic": ""
}

I have checked and no error is shown on a node-red 2.3 server, and i am fairly sure it worked on 3.0 to.

Expected Behavior

Not to show error as using tranform function in test panel worked fine prior to update to 3.1.3

Steps To Reproduce

As described above

Example flow

[
    {
        "id": "d115287648de5277",
        "type": "inject",
        "z": "d1395164b4eec73e",
        "name": "",
        "props": [
            {
                "p": "payload"
            },
            {
                "p": "topic",
                "vt": "str"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "",
        "payload": "[{\"w1\":\"This\",\"w2\":\"is\",\"w3\":\"Big!\"},{\"w1\":\"Big\",\"w2\":\"as\",\"w3\":\"this?\"}]",
        "payloadType": "json",
        "x": 110,
        "y": 2500,
        "wires": [
            [
                "8c8a243c01c3e7b0"
            ]
        ]
    },
    {
        "id": "8c71a0febf7bcd4d",
        "type": "debug",
        "z": "d1395164b4eec73e",
        "name": "debug 8",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "true",
        "targetType": "full",
        "statusVal": "",
        "statusType": "auto",
        "x": 660,
        "y": 2500,
        "wires": []
    },
    {
        "id": "8c8a243c01c3e7b0",
        "type": "change",
        "z": "d1395164b4eec73e",
        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "payload",
                "pt": "msg",
                "to": "$$.payload ~> |$|\t {\"a\":\"a\"}\t|",
                "tot": "jsonata"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 300,
        "y": 2500,
        "wires": [
            [
                "8c71a0febf7bcd4d"
            ]
        ]
    }
]

Environment

• Node-RED version: 3.1.3
• Node.js version: 20.2.0
• npm version: 9.6.6
• Platform/OS: turmux
• Browser: chrome

Start by reproducing the transform expression in the Change node editor's JSONata test panel using the supplied payload and example flow. Trace why the test panel reports the null-property error even though the expression runs successfully, then verify that the panel shows no error and preserves the expected transformed output.