so we change this

example1.php

    public function setRequest($request)
    {
        if (is_string($request)) {
            if (!class_exists($request)) {
                throw new Exception('Class is not exists');
            }
            $request = new $request();
        }
        if (!$request instanceof Request\AbstractRequest) {
            throw new Exception('Invalid request class');
        }

        $this->_request = $request;

        return $this;
    }

example2.php

use \Zend\Loader\Exception\InvalidArgumentException;

/*
some code
*/

    public function setRequest($request)
    {
        if (is_string($request)) {
            if (!class_exists($request)) {
                throw new InvalidArgumentException('Class is not exists');
            }
            $request = new $request();
        }
        if (!$request instanceof Request\AbstractRequest) {
            throw new InvalidArgumentException('Invalid request class');
        }

        $this->_request = $request;

        return $this;
    }

original.php

    public function setRequest($request)
    {
        if (is_string($request)) {
            if (!class_exists($request)) {
                \Zend\Loader::loadClass($request);
            }
            $request = new $request();
        }
        if (!$request instanceof Request\AbstractRequest) {
            throw new Exception('Invalid request class');
        }

        $this->_request = $request;

        return $this;
    }