public function setTimestamp($timestamp = null)
    {
        $this->timestamp = $timestamp;
        if ($timestamp === null) {
            $this->timestamp = new Timestamp();
        }
        return $this;
    }
public function setTimestamp($timestamp = null)
    {
        $this->timestamp = $timestamp;
        if ($timestamp === null) {
            $this->timestamp = new Timestamp();
        }
        return $this;
    }
public function setTimestamp ( $ timestamp = null ) { $ this -> timestamp = $ timestamp ; if ( $ timestamp === null ) { $ this -> timestamp = new Timestamp ( ) ; } return $ this ; }
Set signing timestamp

@param Timestamp|string $timestamp
@return $this
Set signing timestamp