func (u Uint64) Get() (uint64, error) {
	if !u.Present() {
		var zero uint64
		return zero, errors.New("value not present")
	}
	return *u.value, nil
}
Get returns the uint64 value or an error if not present.
package optional
import (
	"encoding/json"
	"errors"
)
type Uint64 struct {
	value *uint64
}
func NewUint64(v uint64) Uint64 {
	return Uint64{&v}
}
func (u *Uint64) Set(v uint64) {
	u.value = &v
}