# Try to get an element, return `null` if the `index` is invalid.
	#
	# ~~~
	# var a = [10,20,30]
	# assert a.get_or_null(1) == 20
	# assert a.get_or_null(3) == null
	# assert a.get_or_null(-1) == null
	# assert a.get_or_null(-10) == null
	# ~~~
	fun get_or_null(index: Int): nullable E
	do
		if index >= 0 and index < length then return self[index]
		return null
	end