Issue #3426100: Move initialization of $existing_mappings to clear phpstan error

tests/src/Functional/FillPdfUploadTestBase.php

@@ -91,11 +91,11 @@ abstract class FillPdfUploadTestBase extends FillPdfTestBase {
   protected function assertUploadPdfFile($op = self::OP_UPLOAD, $filename_preexists = FALSE, FillPdfFormInterface $form = NULL) {
     $previous_file_id = $this->getLastFileId();
 
+    $existing_mappings = [];
     if ($op === self::OP_SAVE) {
       // Record the mappings in the FillPdfFormFields before overwriting the
       // file. We may need to compare them later.
       $existing_fields = $form->getFormFields();
-      $existing_mappings = [];
       foreach ($existing_fields as $existing_field) {
         $existing_mappings[$existing_field->pdf_key->value] = $existing_field->value->value;
       }