fix: handle subscription list api when there are `emqx:subscribe` subscriptions

apps/emqx_management/src/emqx_mgmt_api_subscriptions.erl

@@ -177,7 +177,7 @@ format(WhichNode, {{Topic, _Subscriber}, Options}) ->
     maps:merge(
         #{
             topic => get_topic(Topic, Options),
-            clientid => maps:get(subid, Options),
+            clientid => maps:get(subid, Options, null),
             node => WhichNode
         },
         maps:with([qos, nl, rap, rh], Options)

apps/emqx_management/test/emqx_mgmt_api_subscription_SUITE.erl

@@ -19,6 +19,7 @@
 -compile(nowarn_export_all).
 
 -include_lib("eunit/include/eunit.hrl").
+-include_lib("common_test/include/ct.hrl").
 
 -define(CLIENTID, <<"api_clientid">>).
 -define(USERNAME, <<"api_username">>).
@@ -142,6 +143,18 @@ t_subscription_fuzzy_search(Config) ->
     ?assertEqual(#{<<"page">> => 2, <<"limit">> => 3, <<"hasnext">> => false}, MatchMeta2P2),
     ?assertEqual(1, length(maps:get(<<"data">>, MatchData2P2))).
 
+%% checks that we can list when there are subscriptions made by
+%% `emqx:subscribe'.
+t_list_with_internal_subscription(_Config) ->
+    emqx:subscribe(<<"some/topic">>),
+    QS = [],
+    Headers = emqx_mgmt_api_test_util:auth_header_(),
+    ?assertMatch(
+        #{<<"data">> := [#{<<"clientid">> := null}]},
+        request_json(get, QS, Headers)
+    ),
+    ok.
+
 request_json(Method, Query, Headers) when is_list(Query) ->
     Qs = uri_string:compose_query(Query),
     {ok, MatchRes} = emqx_mgmt_api_test_util:request_api(Method, path(), Qs, Headers),