problem : Trying to get property of non-object in ……

hi,
I get a notice: Trying to get property of non-object in wp-content/themes/tin/libraries/init.php on line 344

this line 344-450 :

if( is_array( $user->roles )) {
    if( in_array( 'administrator', $user->roles )) {
        admin_url();
    } else {
        site_url();
    }
}

anyone can help me? thanks in advance ??