diff --git a/lib/src/helpers.dart b/lib/src/helpers.dart
index c59cdfb..c770e6f 100644
--- a/lib/src/helpers.dart
+++ b/lib/src/helpers.dart
@@ -19,12 +19,12 @@ String getSubProtocol(Serializer serializer) {
 
 String wampErrorString(Error err) {
   String errStr = err.uri;
-  if (err.args.isNotEmpty) {
-    String args = err.args.map((arg) => arg.toString()).join(", ");
+  if (err.args != null) {
+    String args = err.args!.map((arg) => arg.toString()).join(", ");
     errStr += ": $args";
   }
-  if (err.kwargs.isNotEmpty) {
-    String kwargs = err.kwargs.entries.map((entry) => "${entry.key}=${entry.value}").join(", ");
+  if (err.kwargs != null) {
+    String kwargs = err.kwargs!.entries.map((entry) => "${entry.key}=${entry.value}").join(", ");
     errStr += ": $kwargs";
   }
   return errStr;
diff --git a/lib/src/joiner.dart b/lib/src/joiner.dart
index 54240a6..716d918 100644
--- a/lib/src/joiner.dart
+++ b/lib/src/joiner.dart
@@ -23,7 +23,7 @@ class WAMPSessionJoiner {
     WebSocketChannel channel = webSocketChannel(uri, getSubProtocol(_serializer));
     await channel.ready;
 
-    final joiner = Joiner(realm, _serializer, _authenticator);
+    final joiner = Joiner(realm, serializer: _serializer, authenticator: _authenticator);
     channel.sink.add(joiner.sendHello());
 
     var welcomeCompleter = Completer<BaseSession>();