From 8bcf15f391534a00b6ab64798ba503c92d54769c Mon Sep 17 00:00:00 2001
From: zhanghongtong <rory-z@outlook.com>
Date: Thu, 23 Jul 2020 17:17:41 +0800
Subject: [PATCH] fix(emqx_channel): fix some error when properties equal
 undefined

---
 src/emqx_channel.erl | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/emqx_channel.erl b/src/emqx_channel.erl
index 9c295a186..4f9f55d2f 100644
--- a/src/emqx_channel.erl
+++ b/src/emqx_channel.erl
@@ -1247,9 +1247,13 @@ packing_alias(Packet = #mqtt_packet{
               Channel = ?IS_MQTT_V5 = #channel{topic_aliases = TopicAliases, alias_maximum = Limits}) ->
     case find_alias(outbound, Topic, TopicAliases) of
         {ok, AliasId} -> 
+            NProp = case Prop of
+                        undefined -> #{'Topic-Alias' => AliasId};
+                        _ -> maps:merge(Prop, #{'Topic-Alias' => AliasId})
+            end,
             NPublish = Publish#mqtt_packet_publish{
                             topic_name = <<>>,
-                            properties = maps:merge(Prop, #{'Topic-Alias' => AliasId})
+                            properties = NProp
                             },
             {Packet#mqtt_packet{variable = NPublish}, Channel};
         error ->
@@ -1260,9 +1264,13 @@ packing_alias(Packet = #mqtt_packet{
                 true ->
                     NTopicAliases = save_alias(outbound, AliasId, Topic, TopicAliases),
                     NChannel = Channel#channel{topic_aliases = NTopicAliases},
+                    NProp = case Prop of
+                                undefined -> #{'Topic-Alias' => AliasId};
+                                _ -> maps:merge(Prop, #{'Topic-Alias' => AliasId})
+                    end,
                     NPublish = Publish#mqtt_packet_publish{
                                     topic_name = Topic,
-                                    properties = maps:merge(Prop, #{'Topic-Alias' => AliasId})
+                                    properties = NProp
                                     },
                     {Packet#mqtt_packet{variable = NPublish}, NChannel};
                 false -> {Packet, Channel}