Grid/Export/Export.php
public function getParameter($name)
    {
        if (!$this->hasParameter($name)) {
            throw new \InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
        }

        return $this->parameters[$name];
    }
public function getParameter($name)
    {
        if (!$this->hasParameter($name)) {
            throw new \InvalidArgumentException(sprintf('The parameter "%s" must be defined.', $name));
        }

        return $this->parameters[$name];
    }
get parameter.

@return mixed