$re = '/^.+(null)(?!.*\befficient.*)/m';
$str = 'nullPANIFICACAO TOCANTINS LTDA
RELACAO DAS VENDAS POR CLIENTE PERIODO DE 31/05/2020 A 30/06/2020
Cod: 000004 Rota : 032 Nome : MULTI FORMATO DISTRIBUIDORA S/A
N.Fantasia : SUPER NOSSO Pro.:CONTATO
Endereco : RUA ANDRE CAVALCANTI 237 GUTIERREZ
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php