@Override
    public String toString() {
        return isPresent()
                ? String.format("NullableOptional[%s]", this.value)
                : "NullableOptional.empty";
    }
Returns a non-empty string representation of this NullableOptional suitable for
debugging.

@return the string representation of this instance
helper/src/main/java/me/lucko/helper/utils/NullableOptional.java