AttributeError while counting catalog results from an integer index

[hvelarde]

in one of our products (collective.nitf) we have a catalog index based on a field that stores integers (urgency, declared as FieldIndex).

when I add a widget using this field I see an error in the log:

2016-08-25 09:42:30 ERROR Zope.SiteErrorLog 1472128950.560.175418115476 http://localhost:8080/Plone/faceted-search/at_validate_field
Traceback (innermost last):
  Module ZPublisher.Publish, line 138, in publish
  Module ZPublisher.mapply, line 77, in mapply
  Module ZPublisher.Publish, line 48, in call_object
  Module Products.Archetypes.browser.validation, line 22, in __call__
AttributeError: getField

if I use the widget, the results are not filtered; if I set the widget to count the values it breaks the faceted navigation:

2016-08-25 09:41:51 ERROR Zope.SiteErrorLog 1472128911.70.423699787568 http://localhost:8080/Plone/faceted-search/@@faceted_counter
Traceback (innermost last):
  Module ZPublisher.Publish, line 138, in publish
  Module ZPublisher.mapply, line 77, in mapply
  Module ZPublisher.Publish, line 48, in call_object
  Module eea.facetednavigation.caching.nocache, line 12, in replacement
  Module eea.facetednavigation.browser.app.counter, line 76, in __call__
  Module eea.facetednavigation.browser.app.counter, line 57, in query
  Module eea.facetednavigation.widgets.widget, line 457, in count
AttributeError: 'int' object has no attribute 'decode'

running Plone 4.3.10 with plone.app.contenttypes 1.1.1 and collective.nitf 2.0b2 installed.