X     float64
		Id    RawMessage
		IdPtr *RawMessage
		Y     float32
	}
	const want = `{"X":0.1,"Id":null,"IdPtr":null,"Y":0.2}`
	err := Unmarshal([]byte(want), &data)
	if err != nil {
		t.Fatalf("Unmarshal error: %v", err)
	}
	if want, got := "null", string(data.Id); want != got {
		t.Fatalf("Unmarshal:\n\tgot:  %s\n\twant: %s", got, want)
	}
	if data.IdPtr != nil {