Manage None as value of PYSON In

issue11280
review393771002
(grafted from bf883a4cc971cbb9c4654e3685aa54af56ab2548)

--HG--
branch : 6.0

proteus/pyson.py

@@ -509,7 +509,10 @@ class In(PYSON):
 
     @staticmethod
     def eval(dct, context):
-        return dct['k'] in dct['v']
+        if dct['v']:
+            return dct['k'] in dct['v']
+        else:
+            return False
 
 
 class Date(PYSON):