update parser

Author: Alexsey-VR

src/CommandLineParser.php

@@ -16,7 +16,7 @@ public function __construct(mixed $parser = null)
 
         $filename = __DIR__ . "/../docopt.txt";
         if (file_exists($filename)) {
-            $handler = fopen($filename, 'r') ?? NULL;
+            $handler = fopen($filename, 'r') ?? null;
             $filesize = filesize($filename) ?? 0;
             if (!is_null($handler)) {
                 $this->parserDescriptor = fread($handler, $filesize) ?? "";