updateIn doesn't properly handle notSetValue #1657
Description
What happened
updateIn doesn't properly handle notSetValue.
How to reproduce
const { updateIn } = require('immutable')
const original = { x: { y: { z: 123 } } }
const NOT_SET = { NOT_SET: true }
console.log(updateIn(original, ['x', 'y'], NOT_SET, val => NOT_SET)) // { x: { y: { NOT_SET: true } } }Expected the log output to be { x: {} } instead. Is this intended behavior?