Filter interfaces without LAG in custom script

[krasotinpa]

Hi again -

I would like to show in the custom script only interfaces that are not assigned to any LAG.
The code below shows all physical and not mgmt interfaces, but does not filter out assigned to LAG.

Where am I wrong?

class LagInterface(Script):
    class Meta:
        name = "TEST TEST"
        description = "TEST TEST"
        commit_default = False
        scheduling_enabled = False

    device = ObjectVar(
        model=Device,
        required=True,
        label="Switch",
        query_params={
            "role": "switch",
        },
    )
    interfaces = MultiObjectVar(
        model=Interface,
        required=True,
        label="Switch interfaces",
        query_params={
            "device_id": "$device",
            "kind": "physical",
            "mgmt_only": "false",
            "lag__isnull": "true", # <<< This should filter empty LAG but it doesnt
        },
    )