in crates/paimon/src/spec/types.rs [1466:1475]
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
if self.nullable {
serializer.serialize_str(T::NAME)
} else {
serializer.serialize_str(&format!("{} NOT NULL", T::NAME))
}
}