src/Common/Message/AbstractRequest.php
protected function setParameter($key, $value)
    {
        if (null !== $this->response) {
            throw new RuntimeException('Request cannot be modified after it has been sent!');
        }

        return $this->traitSetParameter($key, $value);
    }
protected function setParameter($key, $value)
    {
        if (null !== $this->response) {
            throw new RuntimeException('Request cannot be modified after it has been sent!');
        }

        return $this->traitSetParameter($key, $value);
    }
Set a single parameter

@param string $key The parameter key
@param mixed $value The value to set
@return $this
@throws RuntimeException if a request parameter is modified after the request has been sent.