Issue #3312531: Automated tests are failing

src/OhDearHealthcheckGenerator.php

@@ -71,7 +71,7 @@ class OhDearHealthcheckGenerator {
     $sensor_config = $sensorResult->getSensorConfig();
     $label = $sensor_config->getLabel();
     $shortSummary = $sensor_config->getDescription() ?? '';
-    $notificationMessage = Html::decodeEntities($sensorResult->getMessage());
+    $notificationMessage = Html::decodeEntities($sensorResult->getMessage() ?? '');
     if ($value = $sensorResult->getValue()) {
       $meta = [
         'value' => $value,