checking if array[key] isset? throw: index out of range

if i try to access key in 开发者_如何学JAVAarray which does not exist i get throw: index out of range with a stacktrace.

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

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This accualy works:

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