jsNull

jsNull = 5

Example

function IsConcreteJSONNull(Value: TJSONValue): Boolean;
begin
  Result := Value.ValueType = jsNull;
end;

Usage

jsNull identifies a Velox TJSONNull that always reports null and is serialized as the JSON null literal.

Additional Technical Info

jsNull is ordinal 5 of TJSONValueType and is assigned only to concrete TJSONNull objects. They always return IsNull = True and NotNull = False; writing the inherited null flag cannot change those overridden getters.

The scalar AsString accessor returns an empty string for any value whose IsNull is true, including TJSONNull. Container serializers special-case null and emit the literal null. Consequently, do not use AsString = 'null' to detect this kind. Test ValueType for concrete syntax kind and IsNull when any null-marked scalar should count.

Other conversion accessors deliberately collapse null to defaults: Boolean is false, integer/Int64/double are zero, string is empty, and date/time accessors return the library's null-date value. These defaults do not distinguish null from legitimate zero/false/empty values.

TJSONObject.Values[Name] has a Velox-specific side effect: if the name is missing, the getter adds and returns a named TJSONNull. A read can therefore increase ValueCount and change later serialization. Use Contains/FindValue-style checks when you must not mutate the document.

The parser accepts null case-insensitively, although RFC 8259 requires lowercase. Serializers output lowercase null.

The example is source-reviewed only; no JSON parsing, object mutation, conversion, runtime or image test ran.

Related Code Library entries

• jsString, jsNumber and jsBoolean - scalar kinds with separate mutable null state.
• jsObject - missing-value lookup behavior.
• TJSONValue.IsNull - null-state flag.

External references

• RFC 8259 values and null.

Created 2026-07-15