The RFC says all JSON text must be an array or object, null is a value. JSON text is made up of JSON values.
per the RFC,
"JSON can represent four primitive types (strings, numbers, booleans, and null) and two structured types (objects and arrays)."
"An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array."