How to fix golang sql string conversion scan error

I'm receiving the following error when querying a row in an sqlite3 database:

sql: Scan error on column index 3: converting string "" to a int64: strconv.ParseInt: parsing "": invalid syntax

The query itself works, as it is able to return the queried data. I should note that each row in the database contains several columns with NULL data (only the Id and Email columns are populated). I am struggling to understand why the err occurs and how to resolve it.

The SQL table has the following nine columns:

`0,Id,INTEGER,0,,1
1,Email,TEXT,0,,0
2,Name,TEXT,0,,0
3,Rsvp,INTEGER,0,,0
4,Guests,INTEGER,0,,0
5,Meal0,INTEGER,0,,0
6,Meal1,INTEGER,0,,0
7,Comments,TEXT,0,,0
8,ModifiedAt,TEXT,0,,0`

which are defined in server.go with the following struct (I added the sql.NullString to handle the empty columns):

type User struct {
    Id         int
    Email      string
    Name       sql.NullString
    Rsvp       sql.NullInt64
    Guests     sql.NullInt64
    Meal0      sql.NullInt64
    Meal1      sql.NullInt64
    Comments   sql.NullString
    ModifiedAt sql.NullString
}

the query is from the following handler:

func Rsvp1Handler(w http.ResponseWriter, r *http.Request) {
  email := r.URL.Path[len("/rsvp/"):]
  var user User
  err := userStatement.QueryRow(email).Scan(&user.Id, &user.Email, &user.Name, &user.Rsvp, &user.Guests, &user.Meal0, &user.Meal1, &user.Comments, &user.ModifiedAt)

  switch {
  case err == sql.ErrNoRows:
    log.Println("No user with that ID.")
    w.Header().Set("Content-Type", "text/plain")
    fmt.Fprintf(w, "Email address not found: %s", email)

  case err != nil:
    log.Println(err)
    fmt.Fprintf(w, "Database error:\n", err)
  default:
    log.Println("Query success. Email address: ", email)
    w.Header().Set("Content-Type", "application/json")
    json.NewEncoder(w).Encode(&user)
}

which relies on the following constant and var:

const userSelect  = "SELECT * FROM rsvp WHERE email = ?"
var userStatement   *sql.Stmt

Any help or insight into the error is greatly appreciated!