added helper to work around py3 None sorting

src/z3c/form/util.py

@@ -25,6 +25,7 @@
 import zope.interface
 import zope.contenttype
 import zope.schema
+from functools import total_ordering
 
 from z3c.form import interfaces
 from z3c.form.i18n import MessageFactory as _
@@ -66,6 +67,24 @@ def createId(name):
     id = binascii.hexlify(name.encode('utf-8'))
     return id.decode() if PY3 else id
 
+
+@total_ordering
+class MinType(object):
+    def __le__(self, other):
+        return True
+
+    def __eq__(self, other):
+        return (self is other)
+
+
+def sortedNone(items):
+    if PY3:
+        Min = MinType()
+        return sorted(items, key=lambda x: Min if x is None else x)
+    else:
+        return sorted(items)
+
+
 def createCSSId(name):
     return str(''.join([
                 (char if char in _acceptableChars else

src/z3c/form/util.txt

@@ -557,3 +557,21 @@ Field and context is also overridable:
 
   >>> util.changedWidget(widget, 'foo', field=IPerson['login'], context=p2)
   False
+
+`sortedNone()` function
+------------------------
+
+  >>> util.sortedNone([None, 'a', 'b'])
+  [None, 'a', 'b']
+
+  >>> util.sortedNone([None, 1, 2])
+  [None, 1, 2]
+
+  >>> util.sortedNone([None, True, False])
+  [None, False, True]
+
+  >>> util.sortedNone([['true'], [], ['false']])
+  [[], ['false'], ['true']]
+
+  >>> util.sortedNone([('false',), ('true',), ()])
+  [(), ('false',), ('true',)]

src/z3c/form/widget.py

@@ -430,7 +430,7 @@ def updateWidgets(self):
                 #      always strings as keys, sorting an str(int/date) is lame
                 #      also, newly added item should be the last...
                 try:
-                    items = sorted(self.value)
+                    items = util.sortedNone(self.value)
                 except:
                     # just in case it's impossible to sort don't fail
                     items = self.value