Use Null constant from python-sql for comparisons

issue4143
review13701003

price_list.py

@@ -2,6 +2,7 @@
 #this repository contains the full copyright notices and license terms.
 from decimal import Decimal
 
+from sql import Null
 from simpleeval import simple_eval
 
 from trytond.model import ModelView, ModelSQL, MatchMixin, fields
@@ -99,7 +100,7 @@ class PriceListLine(ModelSQL, ModelView, MatchMixin):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == None, table.sequence]
+        return [table.sequence == Null, table.sequence]
 
     @staticmethod
     def default_formula():

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 = ['simpleeval']
+requires = ['simpleeval', '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))