使用foreach循环创建数组时的未定义错误？

Question

This is my code below but this throws a notice undefined variable pgggo_u_catidexcluder. Not sure why

Error points to

if(is_array($pgggo_u_catidexcluder)){

this the complete code

$pgggo_u_catidexclude = array_map('intval', $pgggo_u_catidexclude);
        foreach ($pgggo_u_catidexclude as $value) {
            $pgggo_u_catidexcluder[] = -1*$value;
        }
        if(is_array($pgggo_u_catidexcluder)){
        $pgggo_u_catidexcluder = implode (", ", $pgggo_u_catidexcluder);
        }else{
            $pgggo_u_catidexcluder = '';
        }