public function required(string $errorId = 'FIELD_EMPTY'): valuereader\CommonValueReader
    {
        if ($this->value->isNull()) {
            return new valuereader\MissingValueReader(
                    function($actualErrorId)
                    {
                        $this->paramErrors->append($this->paramName, $actualErrorId);
                    },
                    $errorId
            );
        }

        return $this;
    }