code: public function fetchFilter(string $key, $default = null, $filter = FILTER_DEFAULT, $options = [])
      {
          $value = $this->fetch($key, $default);
  
          if (!is_array($options) && $options) {
              $options = ['flags' => $options];
          }
  
          if (is_array($value) && !isset($options['flags'])) {
              $options['flags'] = FILTER_REQUIRE_ARRAY;
          }
  
          return filter_var($value, $filter, $options);
      }
docs: Filter value.
  
  @param string $key
  @param mixed|null $default The default value if parameter does not exist
  @param int $filter         FILTER_* constant
  @param array $options      Filter options
  @see http://php.net/manual/en/function.filter-var.php
  @return mixed