Fixed comparison to None warning (closes issue #64).

lib/yaml/representer.py

diff --git a/lib/yaml/representer.py b/lib/yaml/representer.py
index 5f4fc70..1e9fa30 100644
--- a/lib/yaml/representer.py
+++ b/lib/yaml/representer.py
@@ -139,7 +139,7 @@
 class SafeRepresenter(BaseRepresenter):
 
     def ignore_aliases(self, data):
-        if data in [None, ()]:
+        if data is None or data is ():
             return True
         if isinstance(data, (str, unicode, bool, int, float)):
             return True

lib3/yaml/representer.py

diff --git a/lib3/yaml/representer.py b/lib3/yaml/representer.py
index 67cd6fd..33ce9e8 100644
--- a/lib3/yaml/representer.py
+++ b/lib3/yaml/representer.py
@@ -132,7 +132,7 @@
 class SafeRepresenter(BaseRepresenter):
 
     def ignore_aliases(self, data):
-        if data in [None, ()]:
+        if data is None or data is ():
             return True
         if isinstance(data, (str, bytes, bool, int, float)):
             return True