From fd4fbf7ea87bbf55712c92ca5f777d24a35ea999 Mon Sep 17 00:00:00 2001
From: Martin Sumner <martin.sumner@adaptip.co.uk>
Date: Fri, 29 Sep 2017 15:28:17 +0100
Subject: [PATCH] Keep trees empty on merge

Done't blow out a tree unnecessarily on merge
---
 src/leveled_tictac.erl | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/leveled_tictac.erl b/src/leveled_tictac.erl
index 2edd636..39bf983 100644
--- a/src/leveled_tictac.erl
+++ b/src/leveled_tictac.erl
@@ -278,7 +278,14 @@ merge_trees(TreeA, TreeB) ->
         fun(SQN, MergeL2) ->
             L2A = get_level2(TreeA, SQN),
             L2B = get_level2(TreeB, SQN),
-            NewLevel2 = merge_binaries(L2A, L2B),
+            BothEmpty = (L2A == ?EMPTY) and (L2B == ?EMPTY),
+            NewLevel2 = 
+                case BothEmpty of
+                    true ->
+                        ?EMPTY;
+                    false ->
+                        merge_binaries(L2A, L2B)
+                end,
             array:set(SQN, NewLevel2, MergeL2)
         end,
     NewLevel2 = lists:foldl(MergeFun,