# Return the element with the highest value (aka. the mode)
	#
	# ~~~
	# var c = new Counter[String].from(["a", "a", "b", "b", "b", "c"])
	# assert c.max == "b"
	# ~~~
	#
	# If more than one max exists, the first one is returned.
	fun max: nullable E do
		var max: nullable Int = null
		var elem: nullable E = null
		for e in map.keys do
			var v = map[e]
			if max == null or v > max then
				max = v
				elem = e
			end
		end
		return elem
	end