El error que te muestra no importa en lo absoluto, solo tienes que desactivar los notice:
Código PHP:
//Al principio de tu codigo
error_reporting(E_ALL ^ E_NOTICE);
Cita:
Iniciado por php.net Hinweis: Enabling E_NOTICE during development has some benefits. For debugging purposes: NOTICE messages will warn you about possible bugs in your code. For example, use of unassigned values is warned. It is extremely useful to find typos and to save time for debugging. NOTICE messages will warn you about bad style. For example, $arr[item] is better to be written as $arr['item'] since PHP tries to treat "item" as constant. If it is not a constant, PHP assumes it is a string index for the array.