Support child_of/parent_of with None in the value list

This was a implicit behaviour before the changeset 6fefd00369c1.
As a lot of code rely on this behaviour, we make it explicit by adding a test
case.

issue7405
review36251002

trytond/model/fields/many2one.py

@@ -116,7 +116,7 @@ class Many2One(Field):
         cursor = Transaction().connection.cursor()
         table, _ = tables[None]
         name, operator, ids = domain
-        red_sql = reduce_ids(table.id, ids)
+        red_sql = reduce_ids(table.id, (i for i in ids if i is not None))
         Target = self.get_target()
         left = getattr(Target, self.left).sql_column(table)
         right = getattr(Target, self.right).sql_column(table)
@@ -138,8 +138,7 @@ class Many2One(Field):
         target = Target.__table__()
         table, _ = tables[None]
         name, operator, ids = domain
-        ids = set(ids)  # Ensure it is a set for concatenation
-        red_sql = reduce_ids(target.id, ids)
+        red_sql = reduce_ids(target.id, (i for i in ids if i is not None))
 
         if operator.endswith('child_of'):
             tree = With('id', recursive=True)

trytond/tests/test_field_many2one.py

@@ -320,6 +320,25 @@ class FieldMany2OneTestCase(unittest.TestCase):
         "Test search many2one mptt not child of empty"
         self._test_search_not_child_of_empty('test.many2one_mptt')
 
+    @with_transaction()
+    def _test_search_child_of_none(self, model_name):
+        Many2One = Pool().get(model_name)
+        self.create_tree(Many2One)
+
+        result = Many2One.search([
+                ('many2one', 'child_of', [None]),
+                ])
+
+        self.assertListEqual(result, [])
+
+    def test_search_tree_child_of_none(self):
+        "Test search many2one tree child of None"
+        self._test_search_child_of_none('test.many2one_tree')
+
+    def test_search_mptt_child_of_none(self):
+        "Test search many2one mptt child of None"
+        self._test_search_child_of_none('test.many2one_mptt')
+
     @with_transaction()
     def _test_search_parent_of_root1(self, model_name):
         Many2One = Pool().get(model_name)