diff --git a/core/modules/update/tests/src/Kernel/UpdateReportTest.php b/core/modules/update/tests/src/Kernel/UpdateReportTest.php
new file mode 100644
index 00000000000..c7719c14cc1
--- /dev/null
+++ b/core/modules/update/tests/src/Kernel/UpdateReportTest.php
@@ -0,0 +1,57 @@
+<?php
+
+namespace Drupal\Tests\update\Kernel;
+
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests update report functionality.
+ *
+ * @covers template_preprocess_update_report()
+ * @group update
+ */
+class UpdateReportTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'system',
+    'update',
+  ];
+
+  /**
+   * @dataProvider providerTemplatePreprocessUpdateReport
+   */
+  public function testTemplatePreprocessUpdateReport($variables) {
+    \Drupal::moduleHandler()->loadInclude('update', 'inc', 'update.report');
+
+    // The function should run without an exception being thrown when the value
+    // of $variables['data'] is not set or is not an array.
+    template_preprocess_update_report($variables);
+
+    // Test that the key "no_updates_message" has been set.
+    $this->assertArrayHasKey('no_updates_message', $variables);
+  }
+
+  /**
+   * Provides data for testTemplatePreprocessUpdateReport().
+   *
+   * @return array
+   *   Array of $variables for template_preprocess_update_report().
+   */
+  public function providerTemplatePreprocessUpdateReport() {
+    return [
+      '$variables with data not set' => [
+        [],
+      ],
+      '$variables with data as an interger' => [
+        ['data' => 4],
+      ],
+      '$variables with data as a string' => [
+        ['data' => 'I am a string'],
+      ],
+    ];
+  }
+
+}
diff --git a/core/modules/update/update.report.inc b/core/modules/update/update.report.inc
index a60c0d86d37..847f3c28a03 100644
--- a/core/modules/update/update.report.inc
+++ b/core/modules/update/update.report.inc
@@ -20,7 +20,7 @@ use Drupal\update\UpdateManagerInterface;
  *   - data: An array of data about each project's status.
  */
 function template_preprocess_update_report(&$variables) {
-  $data = $variables['data'];
+  $data = isset($variables['data']) && is_array($variables['data']) ? $variables['data'] : [];
 
   $last = \Drupal::state()->get('update.last_check', 0);