Serialize serde_json::Value::Object contains Null/None get error Custom("unsupported value")

[pymongo]

I try below code but got error Err value: Custom("unsupported value")

serde_urlencoded::to_string(&serde_json::json!({
    "limit": serde_json::Value::Null,
    "timestamp": 1700283922524u64 
})).unwrap();

serde_json::Value

impl Serialize for Value {
    #[inline]
    fn serialize<S>(&self, serializer: S) -> result::Result<S::Ok, S::Error>
    where
        S: ::serde::Serializer,
    {
        match self {
            Value::Null => serializer.serialize_unit(),

should serialize Null/None return Ok?

serde_urlencoded/src/ser/part.rs

Lines 114 to 116 in d8bc15d

	fn serialize_unit(self) -> Result<S::Ok, Error> {
	Err(self.sink.unsupported())
	}