private function setField($paramName, $value = false, $isValid = null, $validators = null)
    {
        if (! isset($this->_fields[$paramName])) {
            $this->_fields[$paramName] = array(
                'originalValue' => (isset($this->_params[$paramName])) ? $this->_params[$paramName] : null,
                'value' => (isset($this->_params[$paramName])) ? $this->_params[$paramName] : null,
                'isValid' => true,
                'validators' => array()
            );
        }
        if ($value !== false) {
            $this->_fields[$paramName]['value'] = $value;
        }
        if ($isValid !== null) {
            $this->_fields[$paramName]['isValid'] = $this->_fields[$paramName]['isValid'] && $isValid;
        }
        if ($validators !== null) {
            $this->_fields[$paramName]['validators'] = $validators;
        }
    }