Not a Number

Kinda. nil is a weird value in Go, not quite the same as null or None in JS and Python, respectively. A nil value may or may not be typed and it may or may not be comparable to similar or different types. There is logical consistency to where these scenarios can be hit but it is pretty convoluted and much safer, with fewer footguns to check for nil values before comparison.

I'm other words, in Go (nil == nil) || (nil != nil), depending on the underlaying types. One can always check if a variable has a nil value but may not be able to compare variables if one or more have a nil value. Therefore, it is best to first check for nil values to protect against errors that failure to execute comparisons might cause (anything from incorrect outcome to panic).

ETA: Here's some examples

// this is always possible for a variable that may have a nil value. 
a != nil || a == nil

a = nil
b = nil
// This may or may not be valid, depending on the underlying types.
a != b || a == b

// Better practice for safety is to check for nil first
if a != nil && b != nil {
    if a == b {
        fmt.Println("equal")
    } else {
        fmt.Println("not equal")
    }
} else {
    fmt.Println("a and/or b is nil and may not be comparable")
}