Fatal error: escapeshellarg(): Input string contains NULL bytes

This is maybe more of a PHP question than pdfparser one but here it goes anyway:
Important part of my code:

$parser = new \Smalot\PdfParser\Parser();
$pdf = $parser->parseFile($file_path);
$pages  = $pdf->getPages();
foreach ($pages as $page) {
  $text = $page->getText();
  $stringWithoutNewLine = str_replace("\n"," ",escapeshellarg($text));
  //some more code
}

And this returns the error in the title. Sure enoguh, I think some of the pages in my .pdf have only images, no text.
I would like to get an empty string if there is no text on the page.

Start with the reported call path through Parser::parseFile(), getPages(), and each page's getText() result, then inspect how image-only pages are represented. Reproduce the NULL-byte failure using a PDF page without text and determine the expected empty-string behavior before identifying where a regression test belongs.