diff --git a/htdocs/core/modules/modProduct.class.php b/htdocs/core/modules/modProduct.class.php
index 13e9816008e..001c7759c67 100644
--- a/htdocs/core/modules/modProduct.class.php
+++ b/htdocs/core/modules/modProduct.class.php
@@ -552,6 +552,7 @@ class modProduct extends DolibarrModules
                 )
             );
 
+            if (! is_array($this->import_convertvalue_array[$r])) $this->import_convertvalue_array[$r] = array();
 			$this->import_convertvalue_array[$r] = array_merge($this->import_convertvalue_array[$r], array(
 				'p.fk_unit' => array(
 					'rule' => 'fetchidfromcodeorlabel',