use nullable string in user

internal/database/database.go

@@ -27,7 +27,8 @@ func ConnectDatabase(dbConnString string) {
 		func(name string) ([]byte, error) {
 			return migrations.Asset(name)
 		})
-	db, err := sql.Open("postgres", dbConnString)
+	var err error
+	db, err = sql.Open("postgres", dbConnString)
 	if err != nil {
 		log.Fatal(fmt.Errorf("Can't connect to the database: %w", err))
 	}

internal/database/user.go

@@ -20,7 +20,8 @@ func (s userService) User(id string) (geeksbot.User, error) {
 
 func (s userService) CreateUser(u geeksbot.User) (geeksbot.User, error) {
 	queryString := "INSERT INTO users (id, steam_id, active, staff, admin) VALUES ($1, $2, $3, $4, $5)"
-	_, err := s.db.Exec(queryString, u.ID, u.SteamID, u.IsActive, u.IsStaff, u.IsAdmin)
+	var err error
+	_, err = s.db.Exec(queryString, u.ID, u.SteamID, u.IsActive, u.IsStaff, u.IsAdmin)
 	return u, err
 }