src/AbstractTransport.php
public function setConfig($name, $value)
    {
        if ($name == self::PARAM_FORM || $name == self::PARAM_MULTIPART) {
            return $this;
        }

        if ($name == 'headers' || $name == self::PARAM_FORM || $name == self::PARAM_MULTIPART) {
            if (is_array($value)) {
                $obj = $name == 'headers'
                    ? $this->withHeaders($value)
                    : $this->withParams($value, $name);
                $this->configs = $obj->configs;
                $this->client  = $obj->client;
                $this->request = $obj->request;
            }

            return $this;
        }

        $this->configs[$name] = $value;
        return $this->buildConfigClient();
    }
public function setConfig($name, $value)
    {
        if ($name == self::PARAM_FORM || $name == self::PARAM_MULTIPART) {
            return $this;
        }

        if ($name == 'headers' || $name == self::PARAM_FORM || $name == self::PARAM_MULTIPART) {
            if (is_array($value)) {
                $obj = $name == 'headers'
                    ? $this->withHeaders($value)
                    : $this->withParams($value, $name);
                $this->configs = $obj->configs;
                $this->client  = $obj->client;
                $this->request = $obj->request;
            }

            return $this;
        }

        $this->configs[$name] = $value;
        return $this->buildConfigClient();
    }
Set Config

@param mixed $name
@param mixed $value
@return static