nil detection in Go

I see a lot of code in Go to detect nil, like this:

if err != nil { 
    // handle the error    
}

however, I have a struct like this:

type Config struct {
    host string  
    port float64
}

and config is an instance of Config, when I do:

if config == nil {
}

there is compile error, saying:
cannot convert nil to type Config