Unexpected behavior of `time::serde::rfc3339::option::deserialize()`

[OrangeTux]

When deserializing some data into a struct, serde doesn't care if an field with type Option<T> is available in the source bytes or not.
For example, the following code works fine. It parses an empty json string {} as a Passes instance.

// Relies on serde and serde-json.
// Code runs fine.
use serde::Deserialize;
use serde_json::json;


#[derive(Deserialize, Debug)]
struct Passes {
    attribute: Option<i32>,
}


fn main() {
    let source = json!({});
    let concrete_type: Passes = serde_json::from_value(source).unwrap();
    dbg!(concrete_type);

I would expect the same behavior for something of type Option<time::OffsetDateTime>. But that type behaves different when using the time::serde::rfc3339::option::deserialize. Consider the following code. When you run it, it'll panic. The code tries to deserialize an empty {} as a struct Fails. And that fails. serde claims that fields datetime is missing. Although the attribute being Optional,

/// relies on serde, serde-json and time.

use time::OffsetDateTime;
use serde::Deserialize;
use serde_json::json;


#[derive(Deserialize, Debug)]
struct Fails {
    #[serde(with = "time::serde::rfc3339::option")]
    datetime: Option<OffsetDateTime>,
}

fn main() {
    let source = json!({});
    /// Code panics here.
    let concrete_type: Fails = serde_json::from_value(source).unwrap();
}

The failure is:

thread 'main' panicked at src/main.rs:27:63:
called `Result::unwrap()` on an `Err` value: Error("missing field `datetime`", line: 0, column: 0)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Is this is bug? Shouldn't datetime be set to None when the field is not present input that's passed to serde_jsoin:from_value()?
If so, I'm happy to provide a PR to fix the behavior.

Note, I'm aware that I can work around the issue by changing the field attribute of Fails.datetime from 'm aware that I can work around #[serde(with = "time::serde::rfc3339::option")] to #[serde(with = "time::serde::rfc3339::option", default)]

[jhpratt]

This has been brought up before, and I'm not aware of how to fix it. My recommendation has always been to use #[serde(default)]. If there is a better way, I'm more than happy to review a PR.

[OrangeTux]

Related #562

[OrangeTux]

Thanks for the response. I'll have try to find a fix. Bit since you're aware of the issue and don't know a solution, I'm doubt that I'll fine a solution.