Add #[serde(skip_serializing_if = "Option::is_none")] to all fields

[stefansundin]

Hello,

I think it would be nice if there weren't any null values in my serialized data. After all, if I understand the spec then those keys are not present in the database that the library read, so I feel like it would be best if they were not present in my serialized output at all.

I am unaware if there's a cleaner way to apply the serde attribute other than repeating it like this.

Please let me know if this makes sense or if you want any changes made. Thank you!

[oschwald]

I agree. This makes sense. Too bad there isn't a less verbose way to do this.