"Fetch entity by property" has a configuration and evaluation problem

Had to debug this for some default rules in Commerce Checkout where I'm having to load a user by the e-mail address of an order ($order->mail). The first issue I ran into was that when trying to load a user with the "Fetch entity by property" action, I could not select the mail property of the order to load it by. In fact, all I could select were existing users... the reason being rules_action_entity_query_info_alter() was setting my value parameter to only accept values of the same type as the entity I was trying to load:

/**
 * Info alteration callback for the entity query action.
 */
function rules_action_entity_query_info_alter(&$element_info, RulesAbstractPlugin $element) {
  $element->settings += array('type' => NULL);
  $element_info['parameter']['value']['type'] = $element->settings['type'];
  $element_info['provides']['entity_fetched']['type'] = 'list<' . $element->settings['type'] . '>';
}

Removing the value type adjustment solved the problem for me.

However, in the course of this, I found as well that the evaluation of this action calls the entity_property_query() function and then always uses array_keys() on the return value. The problem is that function can return NULL if you're trying to fetch an entity via a property that doesn't specify a query callback. This was causing a nice red fatal error. My solution was simply to check the type in the action callback on return:

/**
 * Action: Query entities.
 */
function rules_action_entity_query($type, $property, $value, $limit) {
  $return = entity_property_query($type, $property, $value, $limit);
  return array('entity_fetched' => !empty($return) ? array_values($return) : array());
}

The alternative would be to adjust entity_property_query() so it returns an empty array whether there weren't any entities available or it couldn't find a query callback. I suppose you could also just wrap the $return = ... line in an if().

These are both one-liners that I didn't think needed a patch, but I can roll one if you need to review that way.