Concat empty array to nil

Author: fahchen

lib/ltree.ex

@@ -66,6 +66,7 @@ defmodule Hierarch.LTree do
   @doc """
   Join list into a string path
   """
+  def join([]), do: nil
   def join(list) when is_list(list) do
     Enum.join(list, @separator)
   end

test/ltree_test.exs

@@ -50,4 +50,12 @@ defmodule Hierarch.LtreeTest do
       assert ["Top", "Science"] == LTree.split("Top.Science")
     end
   end
+
+  describe "concat/1" do
+    test "works" do
+      assert nil == LTree.concat(nil, nil)
+      assert nil == LTree.concat(nil, "")
+      assert "Top.Science" == LTree.concat("Top.Science", nil)
+    end
+  end
 end