diff --git a/classes/xml/xmlquery/argument/Argument.class.php b/classes/xml/xmlquery/argument/Argument.class.php
index a3ed14a56..2d48a3a48 100644
--- a/classes/xml/xmlquery/argument/Argument.class.php
+++ b/classes/xml/xmlquery/argument/Argument.class.php
@@ -47,6 +47,7 @@
 				$dbParser = XmlQueryParser::getDBParser();
 				return $dbParser->parseExpression($value);                            
                         }  
+                        if(!isset($value) || $value === '') return null;
 			if(in_array($this->type, array('date', 'varchar', 'char','text', 'bigtext'))){
 				if(!is_array($value))
 					$value = '\''.$value.'\'';