Update nullability section

Author: colinhacks

packages/docs/content/json-schema.mdx

@@ -179,16 +179,20 @@ z.undefined();
 // => { type: "null" }
 ```
 
-Similarly, `optional` and `nullable` are made nullable via `oneOf`:
+Similarly, `nullable` is represented via a union with `null`::
 
 ```ts
-z.optional(z.string());
-// => { oneOf: [{ type: "string" }, { type: "null" }] }
-
 z.nullable(z.string());
 // => { oneOf: [{ type: "string" }, { type: "null" }] }
 ```
 
+Optional schemas are represented as-is, though they are decorated with an `optional` annotation.
+
+```ts
+z.optional(z.string());
+// => { type: "string" }
+```
+
 {/* ### Pipes
 
 Pipes contain and input and and output schema. Zod uses the *output schema* for JSON Schema conversion. */}

play.ts

@@ -1,11 +1,6 @@
 import { z } from "zod/v4";
 
-const User = z.object({
-  name: z.string(),
-  get friend() {
-    return User;
-  },
-});
+const User = z.string().optional();
 
 console.dir(z.toJSONSchema(User), { depth: null });
 // => {