Empty fields as facets throws php notice

Issue that looks like that @ #1306496, solved in a similar way.

Notice: Uninitialized string offset: 0 in SearchApiFacetapiTerm->addFacetFilter() (line 73 of /home/xz/web/sites7/all/modules/search_api/contrib/search_api_facetapi/plugins/facetapi/query_type_term.inc). Backtrace:

SearchApiFacetapiTerm->addFacetFilter(Object, 'field_intermediario', '') query_type_term.inc:54
SearchApiFacetapiTerm->execute(Object) adapter.inc:472
FacetapiAdapter->addActiveFilters(Object) search_api_facetapi.module:203
search_api_facetapi_search_api_query_alter(Object, NULL, NULL) module.inc:1017
drupal_alter('search_api_query', Object) query.inc:778
SearchApiQuery->preExecute() query.inc:691
SearchApiQuery->execute() query.inc:235
SearchApiViewsQuery->execute(Object) view.inc:991
view->execute(NULL) view.inc:1011
view->render() views_plugin_display_page.inc:217
views_plugin_display_page->execute() view.inc:1132
view->execute_display('page', Array) views.module:462
views_page('promotori', 'page') 
call_user_func_array('views_page', Array) menu.inc:503
menu_execute_active_handler() index.php:21