vue.js watch param is null in child code example

Example 1: vue watch deep property

watch: {
  item: {
     handler(val){
       // do stuff
     },
     deep: true
  }
}

Example 2: vue watch child property

...
watch:{
    'item.someOtherProp'(newVal){
        //to work with changes in "myArray"
    },
    'item.prop'(newVal){
        //to work with changes in prop
    }
}