Fix

src/lager_logger_formatter.erl

@@ -87,8 +87,10 @@ format(#{msg := {report, _Report}, meta := Metadata} = Event, #{report_cb := Fun
     format(Event#{meta => Metadata#{report_cb => Fun}}, maps:remove(report_cb, Config));
 format(#{level := _Level, msg := {report, Report}, meta := #{report_cb := Fun}} = Event, Config) when is_function(Fun, 1) ->
     case Fun(Report) of
+        {"", []} -> "";
         {Format, Args} when is_list(Format), is_list(Args) ->
             format(Event#{msg => {Format, Args}}, Config);
+        "" -> "";
         String ->
             format(Event#{msg => {string, String}}, Config)
     end;