public function addExtendedSigner(\AgentSIB\Diadoc\Api\Proto\Invoicing\Signers\ExtendedSigner $value)
    {
        if ($this->ExtendedSigner === null) {
            $this->ExtendedSigner = new \Protobuf\MessageCollection();
        }

        $this->ExtendedSigner->add($value);
    }