Fix dialyzer warnings.

src/syn.hrl

@@ -33,7 +33,7 @@
 }).
 -record(syn_groups_table, {
     name = undefined :: any(),
-    pid = undefined :: undefined | pid(),
+    pid = undefined :: atom() | pid(),
     node = undefined :: atom(),
     meta = undefined :: any(),
     monitor_ref = undefined :: atom() | reference()

src/syn_groups.erl

@@ -359,7 +359,7 @@ code_change(_OldVsn, State, _Extra) ->
 %% ===================================================================
 %% Internal
 %% ===================================================================
--spec multicast_join(GroupName :: any(), Pid :: pid(), Meta :: any()) -> ok.
+-spec multicast_join(GroupName :: any(), Pid :: pid(), Meta :: any()) -> pid().
 multicast_join(GroupName, Pid, Meta) ->
     spawn_link(fun() ->
         lists:foreach(fun(RemoteNode) ->
@@ -367,7 +367,7 @@ multicast_join(GroupName, Pid, Meta) ->
         end, nodes())
     end).
 
--spec multicast_leave(GroupName :: any(), Pid :: pid()) -> ok.
+-spec multicast_leave(GroupName :: any(), Pid :: pid()) -> pid().
 multicast_leave(GroupName, Pid) ->
     spawn_link(fun() ->
         lists:foreach(fun(RemoteNode) ->

src/syn_registry.erl

@@ -310,7 +310,7 @@ code_change(_OldVsn, State, _Extra) ->
 %% ===================================================================
 %% Internal
 %% ===================================================================
--spec multicast_register(Name :: any(), Pid :: pid(), Meta :: any()) -> ok.
+-spec multicast_register(Name :: any(), Pid :: pid(), Meta :: any()) -> pid().
 multicast_register(Name, Pid, Meta) ->
     spawn_link(fun() ->
         lists:foreach(fun(RemoteNode) ->
@@ -318,7 +318,7 @@ multicast_register(Name, Pid, Meta) ->
         end, nodes())
     end).
 
--spec multicast_unregister(Name :: any()) -> ok.
+-spec multicast_unregister(Name :: any()) -> pid().
 multicast_unregister(Name) ->
     spawn_link(fun() ->
         lists:foreach(fun(RemoteNode) ->