Address comments

changelog/379.bugfix.rst

@@ -1,2 +1,2 @@
-Attributes of _WARNING_DETAILS are checked to make sure they can be dumped
+Warning attributes are checked to make sure they can be dumped prior to
-prior to serializing the warning for submission to the master node.
+serializing the warning for submission to the master node.

testing/acceptance_test.py

@@ -825,9 +825,8 @@ class TestWarnings:
             # The socket itself will end up attached as a value in
             # _WARNING_DETAIL. We need to test that it is not serialized
             # (it can't be, so the test will fail if we try to).
+            @pytest.mark.filterwarnings('always')  
             def test_func(tmpdir):
-                warnings.resetwarnings()
-                warnings.simplefilter('always', ResourceWarning)
                 abuse_socket()
                 gc.collect()
         """

xdist/remote.py

@@ -224,7 +224,7 @@ def serialize_warning_message(warning_message):
         try:
             dumps(attr)
         except DumpError:
-            result[attr_name] = None
+            result[attr_name] = repr(attr)
         else:
             result[attr_name] = attr
     return result