cubicweb #17050181 TZDatetimeField does not handle unspecified value [validation pending]

This comes from 1694e6e9ff94. I get the following traceback:

2017-01-26 16:02:54 - (cubicweb.web) ERROR: unexpected error while validating form
Traceback (most recent call last):
  File "/opt/local/dlaxalde/datacat/venv/local/lib/python2.7/site-packages/cubicweb/web/views/basecontrollers.py", line 209, in _validate_form
    ctrl.publish(None)
  File "/opt/local/dlaxalde/datacat/venv/local/lib/python2.7/site-packages/cubicweb/web/views/editcontroller.py", line 135, in publish
    self._default_publish()
  File "/opt/local/dlaxalde/datacat/venv/local/lib/python2.7/site-packages/cubicweb/web/views/editcontroller.py", line 201, in _default_publish
    eid = self.edit_entity(formparams)
  File "/opt/local/dlaxalde/datacat/venv/local/lib/python2.7/site-packages/cubicweb/web/views/editcontroller.py", line 273, in edit_entity
    self.handle_formfield(form, field, rqlquery)
  File "/opt/local/dlaxalde/datacat/venv/local/lib/python2.7/site-packages/cubicweb/web/views/editcontroller.py", line 305, in handle_formfield
    for field, value in field.process_posted(form):
  File "/opt/local/dlaxalde/datacat/venv/local/lib/python2.7/site-packages/cubicweb/web/formfields.py", line 501, in process_posted
    value = field.process_form_value(form)
  File "/opt/local/dlaxalde/datacat/venv/local/lib/python2.7/site-packages/cubicweb/web/formfields.py", line 479, in process_form_value
    value = form.formvalues[(self, form)] = self._process_form_value(form)
  File "/opt/local/dlaxalde/datacat/venv/local/lib/python2.7/site-packages/cubicweb/web/formfields.py", line 485, in _process_form_value
    return self._ensure_correctly_typed(form, value)
  File "/opt/local/dlaxalde/datacat/venv/local/lib/python2.7/site-packages/cubicweb/web/formfields.py", line 1030, in _ensure_correctly_typed
    return tz_naive.replace(tzinfo=pytz.utc)
AttributeError: 'NoneType' object has no attribute 'replace'
prioritynormal
typebug
done in3.24.4
load left0.000
closed by#5f886dc718ab [web] Handle unspecified value in TZDatetimeField
patch[web] Handle unspecified value in TZDatetimeField [applied]