diff --git a/src/AbstractDocument.php b/src/AbstractDocument.php
index f119b9e..8cd014e 100644
--- a/src/AbstractDocument.php
+++ b/src/AbstractDocument.php
@@ -551,7 +551,8 @@ public function getValue( $expr, $context = null )
      */
     public function setValue( $expr, $value, $context = null )
     {
-        $this->getElement($expr, $context)->nodeValue = $value;
+        if (!is_null($value))
+            $this->getElement($expr, $context)->nodeValue = $value;
 
         return $this;
     }