So you set a field to `null` using

    { "foo": null }

and you delete a field using

    { "foo": null }

don't you see a bit of an issue there?

as in `{null:null}` ?

won't that set a field called 'null', to the value null?

As in { "foo" : null }

You can interpret a null field the same as a missing field. You only need to worry if you have arbitrary dictionary keys and need to differentiate a null value from an missing key.

> You can interpret a null field the same as a missing field.

Not in the general case no, they are two different states, which may have entirely different semantics.

For instance a missing field can mean "don't touch this field" while a field set to null means "set this field to null".

Some schemas might opt to ignore this distinction and collapse the states, but that is a specific decision, and an express loss of information.

> You only need to worry if you have arbitrary dictionary keys and need to differentiate a null value from an missing key.

There are other situations where that's an issue, like the above, or when you're using the object as a set (which JSON doesn't have), or when you've defined the schema to never have missing fields (but possibly have some set to `null`) so clients will break, ...

Null could imply the field was present and a value not entered or not necessary. Missing could imply the field was never known about at all. The context is important.

Null != missing.