literalized argument name in agavi validator

validator.php

<?php

class YourValidator extends AgaviValidator
{
    public function validate()
    {
        if ($this->hasMultipleArguments()) {
            $this->throwError('multiple_arguments');
            return false;
        }

        // this is done to allow to set a default argument in a validator_definition
        $argument_name = $this->getArgument();
        if (false === $argument_name) {
            $argument_name = $this->getParameter('argument_name');
            $this->arguments = array($argument_name);
        }

        ...
    }
}