/// If you assign `nil` as the value for the given key, the dictionary
/// removes that key and its associated value.

import Foundation
var d: [String: Any?] = ["key": nil]
d.count // 1
d["key"] = nil as Any?
// Commented lines below produce the same effect
// let x: Any? = nil
// d["key"] = x 
d["key"] // nil
d.count // 1

import Foundation
var d: [String: Any?] = ["key": nil]
d.count // 1
d["key"] = nil // Removed `as Any?` fix the problem
d["key"] // nil
d.count // 0

import Foundation
var d: [String: Any?] = ["key": nil]
var n =  NSMutableDictionary(dictionary: d)
n.count // 1
n["key"] = nil as Any? // Even with casting to `Any?` works correctly
n["key"] // nil
n.count // 0