# Search a node by a key or prefix
	#
	# Returns `null` if no node matches `string`.
	private fun search_node(string: nullable Object): nullable TrieNode[E] do
		if string == null then return null
		string = string.to_s
		var children = root.children
		var node = null
		for i in [0..string.length[ do
			var c = string.chars[i]
			if children.has_key(c) then
				node = children[c]
				children = node.children
			else
				node = null
				break
			end
		end
		return node
	end