From 80e2c2c95568d1fedf7ea35504945a90be6afda8 Mon Sep 17 00:00:00 2001
From: JianBo He <heeejianbo@gmail.com>
Date: Wed, 14 Jun 2023 15:14:20 +0800
Subject: [PATCH] fix(http): avoid crash if the old sample data dont contain
 `live_connections`

In version 5.1.0, a new metric called "live_connections" was added. However, we try to merge
some data from the Mria disk table, which may include old data formats.

Therefore, maps:get/3 is needed to avoid crashes.
---
 apps/emqx_dashboard/src/emqx_dashboard_monitor.erl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/apps/emqx_dashboard/src/emqx_dashboard_monitor.erl b/apps/emqx_dashboard/src/emqx_dashboard_monitor.erl
index 97d648d59..9eb5ae8a9 100644
--- a/apps/emqx_dashboard/src/emqx_dashboard_monitor.erl
+++ b/apps/emqx_dashboard/src/emqx_dashboard_monitor.erl
@@ -249,7 +249,7 @@ merge_cluster_sampler_map(M1, M2) ->
             (topics, Map) ->
                 Map#{topics => maps:get(topics, M1)};
             (Key, Map) ->
-                Map#{Key => maps:get(Key, M1) + maps:get(Key, M2)}
+                Map#{Key => maps:get(Key, M1, 0) + maps:get(Key, M2, 0)}
         end,
     lists:foldl(Fun, #{}, ?SAMPLER_LIST).