protected function purgeRuntimeCache($key = null, $namespace = null)
    {
        // Assume will fail
        $result = false;

        if ($namespace !== null && !isset($this->runtimeCache[$namespace])) {
            // Nothing to do is a success when purging ...
            $result = true;

        } else {
            // Hard reset when both null ...
            if ($key === null && $namespace === null) {
                $this->runtimeCache = [];

            } else {
                if ($key === null) {
                    $this->runtimeCache[$namespace] = [];
                } else {
                    unset($this->runtimeCache[$namespace][$key]);
                }

            }
        }

        return $result;
    }