source:
  schema:
    ~$wildchild: {}
  access:
    - location: /
      write:    next != null

expected: {
  "rules":{
    ".write":"((newData.val()!=null))",
    ".read":"false",
    "$wildchild": {
      ".write":"((newData.parent().val()!=null))",
      ".validate":"((newData.parent().val()!=null))",
      ".read":"false"
    }
  }
}