Nil pointer to struct not deep equal to nil?

If I have a struct containing a nil pointer of type A, using reflect.DeepEqual to check if that property is nil will result in false, which strikes me as odd behaviour.

type Container struct {
    O *Obj
}

type Obj struct {
    Message string
}

var c Container
eq := reflect.DeepEqual(c.O, nil)
fmt.Printf("O value: %v, is nil: %t", c.O, eq)
// Prints: "O value: <nil>, is nil: false"

Specifically, I am marshaling a JSON object into a struct, where I would like to test that a specific property is nil when the corresponding JSON structure does not contain it. If reflect.DeepEqual is not the way to go, how should I do this?