Use Null constant from python-sql for comparisons

issue4143
review13701003

bank.py

@@ -1,7 +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 stdnum import iban
-from sql import operators, Literal
+from sql import operators, Literal, Null
 
 from trytond.model import ModelView, ModelSQL, fields
 
@@ -65,7 +65,7 @@ class BankAccountNumber(ModelSQL, ModelView):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == None, table.sequence]
+        return [table.sequence == Null, table.sequence]
 
     @classmethod
     def domain_number(cls, domain, tables):

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-stdnum']
+requires = ['python-stdnum', '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))