In JSON/REST API bindings, where a deserializer maps JSON to language-native object/struct type, I'll often need to know the difference between: {} and

In JSON/REST API bindings, where a deserializer maps JSON to language-native object/struct type, I'll often need to know the difference between: {} and { "foo": null } and { "foo": 42 } So I'll represent that (in e.g. Rust) as: struct Whatever { foo: Option<Option<u32>>, } None means not present, Some(None) means present but null, and Some(Some(42)) means present with a value. I'll often use this in PATCH endpoints, where not-present means to leave the current value alone, null means to unset it, and a value means to set to that value.