AddNull

function AddNull: TJSONValue;

Example

procedure ScriptEvent(var Value: variant);
var
  Values: TJSONArray;
begin
  Values := TJSONArray.Create;
  try
    Values.AddNull;
    Value := Values.AsString;  // Current implementation: [""]
  finally
    Values.Free;
  end;
end;

Usage

AddNull adds a null-marked string node that currently serializes as an empty JSON string instead of null.

Additional Technical Info

Despite its name, AddNull creates a TJSONString, sets IsNull=True, appends it and returns it. The array serializer switches on ValueType; because the node is jsString, it quotes its null-aware blank AsString. The emitted value is therefore "", not the JSON literal null.

This is a material implementation defect. Do not use AddNull when an external contract requires JSON null. A real TJSONNull produced by parsing null has ValueType=jsNull and serializes correctly, but this array-specific surface exposes no direct real-null constructor.

The returned node is owned by the array. Do not free it, and do not retain it after deletion, erase, replacement or parent destruction. IsNull=True on the returned node does not repair the array serialization defect.

External references

• RFC 8259 section 3: JSON values and null

Created 2026-07-20