Fix warning

htdocs/webservices/server_productorservice.php

@@ -154,7 +154,7 @@ if (isset($extrafields->attributes[$elementtype]['label']) && is_array($extrafie
 	}
 }
 
-if (is_array($extrafield_array)) $productorservice_fields = array_merge($productorservice_fields, $extrafield_array);
+if (!empty($extrafield_array) && is_array($extrafield_array)) $productorservice_fields = array_merge($productorservice_fields, $extrafield_array);
 
 // Define other specific objects
 $server->wsdl->addComplexType(