IoT-Agent checks default attributes that are not in the iot payload

I have a test environment where I have configured a service group for the JSON IoT Agent with a legacy expression in it:

{
            "_id": "60acc2d549e4721ae5087356",
            "__v": 0,
            "iotagent": "http://10.0.0.2:4062",
            "apikey": "apikeyTest2",
            "entity_type": "WasteContainer",
            "service_path": "/subservice",
            "service": "service",
            "resource": "/iot/json",
            "description": "IoTAgent JSON - Node.js",
            "protocol": "IoTA-JSON",
            "internal_attributes": [],
            "attributes": [
                {
                    "name": "temperature",
                    "object_id": "t",
                    "type": "Number"
                },
                {
                    "name": "fillingLevel",
                    "expression": "${@level/100}",
                    "type": "Number"
                }
            ],
            "lazy": [],
            "static_attributes": [],
            "commands": []
        }

Apart from that I register manually a device with a "jexl" as expression language:

curl --location --request POST 'https://host/iot/devices' \
--header 'Fiware-Service: service' \
--header 'Fiware-ServicePath: /subservice' \
--header 'X-Auth-Token: gAAAAABgrQm..._R8r98aeNWQ' \
--header 'Content-Type: application/json' \
--data-raw '{
  "devices": [
    {
      "device_id": "deviceJSON1",
      "entity_name": "device:entity01",
      "entity_type": "device",
      "expressionLanguage": "jexl",
      "attributes": [
        { 
          "object_id": "b",
          "name": "position", 
          "type": "Number",
          "expression": "(a+b)"
        }
      ],
      "protocol": "IoTA-JSON",
      "transport": "HTTP"
    }
  ]
}
'

Then I send data from the device using the apikey of the previous service group, but without using any attribute configured there:

curl --location --request POST 'http://host/iot/json?k=apikeyTest2&i=deviceJSON1&getCmd=0' \
--header 'Content-Type: application/json' \
--data-raw '{
    "a": 4,
    "b": 5
}'

The response is 400 Bad Request:

{
    "name": "INVALID_EXPRESSION",
    "message": "Invalid expression in evaluation [${@level/100}]"
}

Is this the expected result or should the agent try to use the "jexl" to transform the payload as there is not level attribute in the iot data?

To solve this I can create another service group with a different apikey and without default attributes, but just wanted to know if the result was the expected.