Add condition to handle when mqx_topic_alias do not exist

src/emqx_mqtt_caps.erl

@@ -69,6 +69,8 @@ do_check_pub(Props = #{ topic_alias := TopicAlias}, [{max_topic_alias, MaxTopicA
     end;
 do_check_pub(#{retain := true}, [{mqtt_retain_available, false}|_Caps]) ->
     {error, ?RC_RETAIN_NOT_SUPPORTED};
+do_check_pub(Props, [{max_topic_alias, _} | Caps]) ->
+    do_check_pub(Props, Caps);
 do_check_pub(Props, [{mqtt_retain_available, _}|Caps]) ->
     do_check_pub(Props, Caps).
 

test/emqx_mqtt_caps_SUITE.erl

@@ -63,10 +63,12 @@ t_check_pub(_) ->
     {ok, _} = emqx_zone:start_link(),
     PubCaps = #{
         max_qos_allowed => ?QOS_1,
-        mqtt_retain_available => false
+        mqtt_retain_available => false,
+        max_topic_alias => 4
     },
     emqx_zone:set_env(zone, '$mqtt_pub_caps', PubCaps),
     timer:sleep(100),
+    ct:log("~p", [emqx_mqtt_caps:get_caps(zone, publish)]),
     BadPubProps1 = #{
         qos => ?QOS_2,
         retain => false
@@ -77,6 +79,12 @@ t_check_pub(_) ->
         retain => true
     },
     {error, ?RC_RETAIN_NOT_SUPPORTED} = emqx_mqtt_caps:check_pub(zone, BadPubProps2),
+    BadPubProps3 = #{
+        qos => ?QOS_1,
+        retain => false,
+        topic_alias => 5
+    },
+    {error, ?RC_TOPIC_ALIAS_INVALID} = emqx_mqtt_caps:check_pub(zone, BadPubProps3),
     PubProps = #{
         qos => ?QOS_1,
         retain => false