diff --git a/core/modules/system/tests/src/Functional/FileTransfer/TestFileTransfer.php b/core/modules/system/tests/src/Functional/FileTransfer/TestFileTransfer.php
index f9806fd8b1339212696bbe6691d7ec552aa63add..1860812babf14fdd6096b0ee905404fd6c9a5178 100644
--- a/core/modules/system/tests/src/Functional/FileTransfer/TestFileTransfer.php
+++ b/core/modules/system/tests/src/Functional/FileTransfer/TestFileTransfer.php
@@ -8,10 +8,26 @@
  * Mock FileTransfer object for test case.
  */
 class TestFileTransfer extends FileTransfer {
-  protected $host = NULL;
-  protected $username = NULL;
-  protected $password = NULL;
-  protected $port = NULL;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $host = '';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $username = '';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $password = '';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $port = 0;
 
   /**
    * This is for testing the CopyRecursive logic.