检查是否设置了array [key]？ 抛出：索引超出范围

if i try to access key in array which does not exist i get throw: index out of range with a stacktrace.

How do i check if tmp[key] "is set" ?

This accualy works:

if len(url) > 1 {
    tmp := strings.Split(url[1],"=",0);
    if len(tmp) >1{
        sess = tmp[1];
    }
}