php / xslt想要一个源文档

i getting this error by reloading the page in the error.log:

Either a source document, an initial template or an initial function must be specified

Here my PHP Code:

<?php
// INITIALIZE PROCESSOR
$saxonProc = new Saxon\SaxonProcessor();
$xsltProc = $saxonProc->newXsltProcessor();

$lang = $_GET['lang'];
$rubrik = $_GET['rubrik'];
$seite = $_GET['seite'];

// LOAD XSLT SCRIPT
$xslFile = "../ressources/xslt/transform_article_partials_to_html.xslt";
$xsltProc->compileFromFile($xslFile); 

// SET PARAMS
$dir = __DIR__ . "/articles/" . $lang;
$filename = "{$rubrik}_{$seite}.html";
$filelist = scandir($dir, 1);


$xdmvalue = $saxonProc->createAtomicValue($filename);
$xsltProc->setParameter("articlePfad", $xdmvalue);

$xdmvalue = $saxonProc->createAtomicValue($lang);
$xsltProc->setParameter("lang", $xdmvalue);

// LOAD SOURCE XML
if($seite == null) {
  $filename = "{$rubrik}.html";
  if(in_array($filename, $filelist)) {
    $xmlFile = $dir . "/" . $filename;    
  } else {
    echo "404";
    exit;
  }
} else if(isset($seite) && isset($rubrik)){
  if(in_array($filename, $filelist)) {
    $xmlFile = $dir . "/" . $filename;
  } else {
    echo "404";
  }
}

$xsltProc->setSourceFromFile($xmlFile);

// RUN TRANSFORMATION    
$result = $xsltProc->transformToString();

echo $result;

// RELEASE RESOURCES
$xsltProc->clearParameters();
$xsltProc->clearProperties();

unset($xsltProc);
unset($saxonProc);   
?>

I dont know where is the error. I dont know if this error brokes some, because it works also with the error. On google i have found nothing to this error.