diff --git a/src/mg/PAGI/Node/Node.php b/src/mg/PAGI/Node/Node.php
index 40f30b8..315b047 100644
--- a/src/mg/PAGI/Node/Node.php
+++ b/src/mg/PAGI/Node/Node.php
@@ -503,10 +503,12 @@ public function validate()
                 $onError = $data['soundOnError'];
                 if (is_array($onError)) {
                     foreach ($onError as $msg) {
-                        $this->addPrePromptMessage($msg);
+                        if ($msg!=null)
+                            $this->addPrePromptMessage($msg);
                     }
                 } else {
-                    $this->addPrePromptMessage($onError);
+                    if ($onError!=null)
+                        $this->addPrePromptMessage($onError);
                 }
                 return false;
             }