list_boolean defaults produce an empty value list for list_allowed_values

Funny one with an easy workaround, but worth reporting.

Steps to replicate:

1) Create a Boolean field and leave the label values empty.
2) Create a view and try setting a filter with this.

The list appears empty, when it actually contains two empty values:

class views_handler_filter_field_list {
  function get_value_options() {
    $field = field_info_field($this->definition['field_name']);
    $this->value_options = list_allowed_values($field);
    // $this->value_options == array(0 => '', 1=> '')
  }
}

Workaround is to define two values, which can be 0 & 1 and the array values are populated with this.

The issue itself is a core issue, example fix below, but I am guessing this will never be resolved in D7 :(

function list_allowed_values($field, $instance = NULL, $entity_type = NULL, $entity = NULL) {
  $allowed_values = &drupal_static(__FUNCTION__, array());

  if (!isset($allowed_values[$field['id']])) {
    $function = $field['settings']['allowed_values_function'];
    // If $cacheable is FALSE, then the allowed values are not statically
    // cached. See list_test_dynamic_values_callback() for an example of
    // generating dynamic and uncached values.
    $cacheable = TRUE;
    if (!empty($function) && function_exists($function)) {
      $values = $function($field, $instance, $entity_type, $entity, $cacheable);
    }
    else {
      $values = $field['settings']['allowed_values'];
+      if ($field['type'] == 'list_boolean') {
+        foreach ($values as $key => $value) {
+          if (!strlen($value)) {
+            $value = $key;
+          }
+        }
+      }
    }