public function process()
    {
        parent::process();

        if ($this->value === null) {
            return;
        }

        $this->value = trim($this->value);

        if ($this->value == '') {
            $this->value = null;
            return;
        }

        if (!$this->validateUri($this->value)) {
            if (
                $this->validateUri($this->default_scheme . '://' . $this->value)
            ) {
                if ($this->scheme_required) {
                    $this->addMessage(
                        $this->getValidationMessage('scheme-required')
                    );
                } else {
                    $this->value = $this->default_scheme . '://' . $this->value;
                }
            } else {
                $this->addMessage($this->getValidationMessage('invalid-uri'));
            }
        }
    }