Unmarshalling and marshalling types in the null package isn't symmetric. For example:

type T struct {
  Name null.String
}

in := []byte(`{"Name":""}`)
var t T
json.Unmarshal(in, &t)
fmt.Printf("%+v\n", t) // => {Name:{NullString:{String: Valid:false}}}
out, _ := json.Marshal(t)
fmt.Println(string(out)) // => {"Name":null}

Why not have in unmarshal to {Name:{NullString:{String: Valid:true}}}? In addition to clearing up the issue shown above it would make the null package incredibly useful for the common issue of how to determine if a RESTful request intends to set a value to the zero value or if it just wasn't included in the request (a PATCH-like request).

Right now the common recommendation is to use pointers for the fields in your structs as described here, but I'd much prefer using the null package for this if I could.

Let me know what you think. I'm happy to create a PR for this if you think this idea has legs.