Fatal error: Uncaught TypeError: NFePHP\NFe\Convert::isNFe(): Argument #1 ($txt) must be of type string, null given, called in /home/reve/serv.infotechposse.com.br/src/Convert.php on line 75 and defined in /home/reve/serv.infotechposse.com.br/src/Convert.php:139 Stack trace: #0 /home/reve/serv.infotechposse.com.br/src/Convert.php(75): NFePHP\NFe\Convert->isNFe() #1 /home/reve/serv.infotechposse.com.br/examples/5.0testConvert.php(11): NFePHP\NFe\Convert->toXml() #2 {main} thrown in /home/reve/serv.infotechposse.com.br/src/Convert.php on line 139