Issue #3333298: Do not pass NULL to in_array() in PdftkPdfBackend

src/Plugin/PdfBackend/PdftkPdfBackend.php

@@ -142,7 +142,7 @@ class PdftkPdfBackend extends PdfBackendBase implements ContainerFactoryPluginIn
       }
       // Separate the data key from the data value.
       [$key, $value] = explode(':', $lineitem);
-      if (in_array($key, array_keys($data_fields_map), NULL)) {
+      if (in_array($key, array_keys($data_fields_map))) {
         // Trim spaces.
         $fields[$fieldindex][$data_fields_map[$key]] = trim($value);
       }