Use Null constant from python-sql for comparisons

issue4143
review13701003

address.py

@@ -1,6 +1,8 @@
 #This file is part of Tryton.  The COPYRIGHT file at the top level of
 #this repository contains the full copyright notices and license terms.
 'Address'
+from sql import Null
+
 from trytond.model import ModelView, ModelSQL, fields
 from trytond.pyson import Eval, If
 from trytond.transaction import Transaction
@@ -61,7 +63,7 @@ class Address(ModelSQL, ModelView):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == None, table.sequence]
+        return [table.sequence == Null, table.sequence]
 
     @staticmethod
     def default_active():

contact_mechanism.py

@@ -1,5 +1,7 @@
 #This file is part of Tryton.  The COPYRIGHT file at the top level of
 #this repository contains the full copyright notices and license terms.
+from sql import Null
+
 from trytond.model import ModelView, ModelSQL, fields
 from trytond.pyson import Eval
 from trytond.transaction import Transaction
@@ -102,7 +104,7 @@ class ContactMechanism(ModelSQL, ModelView):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == None, table.sequence]
+        return [table.sequence == Null, table.sequence]
 
     @staticmethod
     def default_type():

setup.py

@@ -41,7 +41,7 @@ if minor_version % 2:
         'hg+http://hg.tryton.org/modules/%s#egg=%s-%s' % (
             name[8:], name, version))
 
-requires = ['python-sql']
+requires = ['python-sql >= 0.4']
 for dep in info.get('depends', []):
     if not re.match(r'(ir|res|webdav)(\W|$)', dep):
         requires.append(get_require_version('trytond_%s' % dep))