final public static function format_properties($properties) {
        foreach ($properties as $property => $definition) {
            // Ensures that null is set to its default.
            if (!isset($definition['null'])) {
                $properties[$property]['null'] = NULL_NOT_ALLOWED;
            }
            if (!isset($definition['description'])) {
                $properties[$property]['description'] = $property;
            }

            // If an array is provided, it may be a nested array that is unformatted so rinse and repeat.
            if (is_array($definition['type'])) {
                $properties[$property]['type'] = static::format_properties($definition['type']);
            }
        }
        return $properties;
    }