[web] Don't raise ProcessFormError if there is no value specified a03376213747 introduced a slight modification in None / empty string values and with it a regression where an exception is raised on empty values, while we should simply consider no value is specified and return None.

.. _appobject_module:

:mod:`cubicweb.appobject`
=========================

.. automodule:: cubicweb.appobject

   .. autoclass:: AppObject
      :show-inheritance:
      :members: