add exception handeling for warning serialization issues

xdist/remote.py

@@ -182,7 +182,7 @@ def serialize_warning_message(warning_message):
         message_module = type(warning_message.message).__module__
         message_class_name = type(warning_message.message).__name__
         message_args = warning_message.message.args
-        message_str = None
+        message_str = str(warning_message.message)
     else:
         message_str = warning_message.message
         message_module = None

xdist/workermanage.py

@@ -426,7 +426,10 @@ def unserialize_warning_message(data):
     if data["message_module"]:
         mod = importlib.import_module(data["message_module"])
         cls = getattr(mod, data["message_class_name"])
-        message = cls(*data["message_args"])
+        try:
+            message = cls(*data["message_args"])
+        except TypeError:
+            message = Warning(data["message_str"])
     else:
         message = data["message_str"]