queue_topology should not return undefined for members

it's easier to deal with the result if members is an empty
list than when it is either a list or `undefined`.

Author: mkuratczyk

deps/rabbit/src/rabbit_amqp_management.erl

@@ -440,13 +440,9 @@ encode_queue(Q, NumMsgs, NumConsumers) ->
                {{utf8, <<"type">>}, {utf8, rabbit_queue_type:to_binary(QType)}},
                {{utf8, <<"arguments">>}, QArgs}
               ],
-    KVList1 = if is_list(Replicas) ->
-                     [{{utf8, <<"replicas">>},
-                       {array, utf8, [{utf8, atom_to_binary(R)} || R <- Replicas]}
-                      } | KVList0];
-                 Replicas =:= undefined ->
-                     KVList0
-              end,
+    KVList1 = [{{utf8, <<"replicas">>},
+                {array, utf8, [{utf8, atom_to_binary(R)} || R <- Replicas]}
+               } | KVList0],
     KVList = case Leader of
                  undefined ->
                      KVList1;
@@ -459,7 +455,7 @@ encode_queue(Q, NumMsgs, NumConsumers) ->
 
 %% The returned Replicas contain both online and offline replicas.
 -spec queue_topology(amqqueue:amqqueue()) ->
-    {Leader :: undefined | node(), Replicas :: undefined | [node(),...]}.
+    {Leader :: undefined | node(), Replicas :: [node(),...]}.
 queue_topology(Q) ->
     Type = amqqueue:get_type(Q),
     Type:queue_topology(Q).

deps/rabbit/src/rabbit_queue_type.erl

@@ -275,7 +275,7 @@
     ok.
 
 -callback queue_topology(amqqueue:amqqueue()) ->
-    {Leader :: undefined | node(), Replicas :: undefined | [node(),...]}.
+    {Leader :: undefined | node(), Replicas :: [node(),...]}.
 
 -spec discover(binary() | atom()) -> queue_type().
 discover(<<"undefined">>) ->

deps/rabbitmq_mqtt/src/rabbit_mqtt_qos0_queue.erl

@@ -305,7 +305,7 @@ state_info(A1) ->
     ?UNSUPPORTED([A1]).
 
 -spec queue_topology(amqqueue:amqqueue()) ->
-    {Leader :: undefined | node(), Replicas :: undefined | [node(),...]}.
+    {Leader :: undefined | node(), Replicas :: [node(),...]}.
 queue_topology(Q) ->
     Pid = amqqueue:get_pid(Q),
     Node = node(Pid),