Merge branch '4.4' into 5.2

* 4.4:
  fix tests (ter)
  Fix tests (bis)
  [travis] fix travis hopefuly
  [Security] Fix SerializableUser fixture
  [FrameworkBundle][WebProfilerBundle] Don't pass null to string parameters

Author: nicolas-grekas

Console/Descriptor/XmlDescriptor.php

@@ -315,7 +315,7 @@ private function getContainerDefinitionDocument(Definition $definition, string $
             $descriptionXML->appendChild($dom->createCDATASection($classDescription));
         }
 
-        $serviceXML->setAttribute('class', $definition->getClass());
+        $serviceXML->setAttribute('class', $definition->getClass() ?? '');
 
         if ($factory = $definition->getFactory()) {
             $serviceXML->appendChild($factoryXML = $dom->createElement('factory'));
@@ -341,7 +341,7 @@ private function getContainerDefinitionDocument(Definition $definition, string $
         $serviceXML->setAttribute('abstract', $definition->isAbstract() ? 'true' : 'false');
         $serviceXML->setAttribute('autowired', $definition->isAutowired() ? 'true' : 'false');
         $serviceXML->setAttribute('autoconfigured', $definition->isAutoconfigured() ? 'true' : 'false');
-        $serviceXML->setAttribute('file', $definition->getFile());
+        $serviceXML->setAttribute('file', $definition->getFile() ?? '');
 
         $calls = $definition->getMethodCalls();
         if (\count($calls) > 0) {