{
  "name": "optional",
  "tree": {
    "$className": "Folder",
    "foo-required": {
      "$path": "foo.txt"
    },
    "foo-optional":{
      "$path": { "optional": "foo.txt" }
    },
    "bar-optional":{
      "$path": { "optional": "bar.txt" }
    }
  }
}