diff --git a/htdocs/core/lib/json.lib.php b/htdocs/core/lib/json.lib.php
index 0704f035848..94842975377 100644
--- a/htdocs/core/lib/json.lib.php
+++ b/htdocs/core/lib/json.lib.php
@@ -206,13 +206,14 @@ if (! function_exists('json_decode'))
  * Implement json_decode for PHP that does not support it
  *
  * @param	string	$json		Json encoded to PHP Object or Array
- * @param	bool	$assoc		False return an object, true return an array
+ * @param	bool	$assoc		False return an object, true return an array. Try to always use it with true !
  * @return 	mixed				Object or Array
  */
 function dol_json_decode($json, $assoc=false)
 {
 	$comment = false;
 
+    $out='';
 	$strLength = strlen($json);    // Must stay strlen and not dol_strlen because we want technical length, not visible length
 	for ($i=0; $i<$strLength; $i++)
 	{