Retrieve an Object stored via []= function

Property definitions

android $ Intent :: []
	# Retrieve an `Object` stored via `[]=` function
	fun [](name: String): nullable Object
	do
		var serialized_string = self.extra_string(name)
		if serialized_string == "" then return null

		var deserializer = new JsonDeserializer(serialized_string)
		return deserializer.deserialize
	end
lib/android/intent/intent_api10.nit:1283,2--1291,4