Correction for warning:

"/osv/orm.py:1964: FutureWarning: The behavior of this method will
change in future versions. Use specific 'len(elem)' or 'elem is not
None' test instead.
  if next:"

trytond/osv/orm.py

@@ -1961,7 +1961,7 @@ class ORM(object):
                     elif pos == 'after':
                         parent = element.getparent()
                         next = element.getnext()
-                        if next:
+                        if next is not None:
                             for child in element2:
                                 index = parent.index(next)
                                 parent.insert(index - 1, child)