Empty fulltext keys cause fatal error

steps to reproduce:

1. install fresh D7, then views UI, search_api, search_api_db, search_api_views.
2. create a search server at admin/config/search/search_api/add_server, choose database as type.
3. enable the default node index.
4. go to views settings at admin/structure/views/settings, and uncheck live preview settings, and save.
5. create a view, select 'Default node index' from the show list, give it a name, all else defaults, click 'Continue and edit'.
6. click the 'add' button for filter criteria, and select 'Search: Fulltext search', choose 'Title' under 'Searched fields', save.
7. click the 'add' button for filter criteria, and select 'Search: Fulltext search', choose 'The main body text' under 'Searched fields', save.
8. Save the view, kaboom.

Below is the exported view, should hopefully help with testing:

$view = new view;
$view->name = 'test_text_bug';
$view->description = '';
$view->tag = 'default';
$view->base_table = 'search_api_index_default_node_index';
$view->human_name = 'test text bug';
$view->core = 7;
$view->api_version = '3.0';
$view->disabled = FALSE; /* Edit this to true to make a default view disabled initially */

/* Display: Master */
$handler = $view->new_display('default', 'Master', 'default');
$handler->display->display_options['title'] = 'test text bug';
$handler->display->display_options['access']['type'] = 'none';
$handler->display->display_options['cache']['type'] = 'none';
$handler->display->display_options['query']['type'] = 'views_query';
$handler->display->display_options['exposed_form']['type'] = 'basic';
$handler->display->display_options['pager']['type'] = 'full';
$handler->display->display_options['pager']['options']['items_per_page'] = '10';
$handler->display->display_options['style_plugin'] = 'default';
$handler->display->display_options['row_plugin'] = 'entity';
/* Field: Node: Node ID */
$handler->display->display_options['fields']['nid']['id'] = 'nid';
$handler->display->display_options['fields']['nid']['table'] = 'search_api_index_default_node_index';
$handler->display->display_options['fields']['nid']['field'] = 'nid';
/* Filter criterion: Search: Fulltext search */
$handler->display->display_options['filters']['search_api_views_fulltext']['id'] = 'search_api_views_fulltext';
$handler->display->display_options['filters']['search_api_views_fulltext']['table'] = 'search_api_index_default_node_index';
$handler->display->display_options['filters']['search_api_views_fulltext']['field'] = 'search_api_views_fulltext';
$handler->display->display_options['filters']['search_api_views_fulltext']['fields'] = array(
  'title' => 'title',
);
/* Filter criterion: Search: Fulltext search */
$handler->display->display_options['filters']['search_api_views_fulltext_1']['id'] = 'search_api_views_fulltext_1';
$handler->display->display_options['filters']['search_api_views_fulltext_1']['table'] = 'search_api_index_default_node_index';
$handler->display->display_options['filters']['search_api_views_fulltext_1']['field'] = 'search_api_views_fulltext';
$handler->display->display_options['filters']['search_api_views_fulltext_1']['fields'] = array(
  'body:value' => 'body:value',
);

/* Display: Page */
$handler = $view->new_display('page', 'Page', 'page');
$handler->display->display_options['path'] = 'test-text-bug';

the code flow goes something like this, getting stuck in a loop in SearchApiDbService::createKeysQuery():

call_user_func_array --> views_page --> view::execute_display --> views_plugin_display_page::execute --> view::render --> view::execute --> SearchApiViewsQuery::execute --> SearchApiQuery::execute --> SearchApiServer::search --> SearchApiDbService::search --> SearchApiDbService::createFilterCondition --> SearchApiDbService::createFilterCondition --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery --> SearchApiDbService::createKeysQuery