public function setNumber( $number )
    {
        if (empty( $number )) {
            throw new InvalidArgumentException( 'Number is empty!' );
        }

        $this->number = (string)$number;

        return $this;
    }
public function setNumber( $number )
    {
        if (empty( $number )) {
            throw new InvalidArgumentException( 'Number is empty!' );
        }

        $this->number = (string)$number;

        return $this;
    }
@param  string $number

@return $this