diff --git a/src/ORM/SalsifyIDExtension.php b/src/ORM/SalsifyIDExtension.php
index d9c4cbd..7a422ff 100644
--- a/src/ORM/SalsifyIDExtension.php
+++ b/src/ORM/SalsifyIDExtension.php
@@ -128,6 +128,8 @@ public function onBeforeWrite()
     {
         parent::onBeforeWrite();
 
-        $this->owner->SalsifyID = trim($this->owner->SalsifyID);
+        if ($this->owner->SalsifyID !== null) {
+            $this->owner->SalsifyID = trim($this->owner->SalsifyID);
+        }
     }
 }