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20130901 (Sunday, 01 September 2013)
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Continued to test and update :func:`lino_welfare.migrate.migrate_from_1_1_8`.

Continued inspirational work on  :mod:`lino.utils.actordoc`.

Found a subtle (internal) bug:

When a :class:`ChoiceListField <lino.core.choicelists.ChoiceListField>` is empty
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The :class:`welfare.pcsw.Clients` table showed also "Former" Clients
at the very first request. A simple Refresh caused it to become 
"correct" showing only active clients.

This was because an empty :class:`ChoiceListField <lino.core.choicelists.ChoiceListField>` was sometimes an empty string 
(``''``) and sometimes ``None``.
In get_request_queryset I tested for 
``ar.param_values.client_state is None``.
The application code was right: 
a 
:class:`ChoiceListField <lino.core.choicelists.ChoiceListField>`
with `blank=True` should never have an empty string as value.
Solved by setting `empty_strings_allowed = False` on 
:class:`ChoiceListField <lino.core.choicelists.ChoiceListField>`.