{
   "blockOptions":{
        "method":{
            "args":{
                "blocks":"blocks"
            },
            "name":"function"
        },
        "function": {
            "latch":{
                "enabled": true
            }
        }
    },
    "blockType":"when",
    "fields":[
        {
            "name":"blocks",
            "type":"blocks",
            "value": [
                __SINGLE_WHEN_BLOCK__
            ]
        }
    ]
}

Here, the stands for any valid when block, like a final event or a logical operator. But, the only child can be passed.