framework/data/Pagination.php
protected function getQueryParam($name, $defaultValue = null)
    {
        if (($params = $this->params) === null) {
            $request = Yii::$app->getRequest();
            $params = $request instanceof Request ? $request->getQueryParams() : [];
        }

        return isset($params[$name]) && is_scalar($params[$name]) ? $params[$name] : $defaultValue;
    }
protected function getQueryParam($name, $defaultValue = null)
    {
        if (($params = $this->params) === null) {
            $request = Yii::$app->getRequest();
            $params = $request instanceof Request ? $request->getQueryParams() : [];
        }

        return isset($params[$name]) && is_scalar($params[$name]) ? $params[$name] : $defaultValue;
    }
Returns the value of the specified query parameter.
This method returns the named parameter value from [[params]]. Null is returned if the value does not exist.
@param string $name the parameter name
@param string $defaultValue the value to be returned when the specified parameter does not exist in [[params]].
@return string the parameter value