oneOf/anyOf doesn't seem to work with objects

🐛 Bug Report

oneOf/anyOf doesn't seem to work with objects.

To Reproduce

The following schema models a union type, i.e. in TypeScript terms:

type Foo = { foo: string, baz: string };
type Bar = { bar: string, baz: string };
type FooBar = Foo | Bar;

const fastJson = require("fast-json-stringify");

const schemaFoo = {
  properties: {
    foo: { type: "string" },
    baz: { type: "string" },
  },
  required: ["foo", "baz"],
};

const schemaBar = {
  properties: {
    bar: { type: "string" },
    baz: { type: "string" },
  },
  required: ["bar", "baz"],
};

const stringify = fastJson({
  type: "object",
  anyOf: [schemaFoo, schemaBar],
});

console.log(stringify({ foo: "foo", baz: "baz" }));
console.log(stringify({ bar: "bar", baz: "baz" }));

Output:

{}
{}

Expected behavior

Since both objects match the schema, both should be stringified.

Your Environment

• node version: v14.16.0
• fastify version: 3.13.0
• fast-json-stringify: 2.4.2
• os: Ubuntu 18.04