Fix serialization logic

src/serializerCompiler.test.ts

@@ -74,6 +74,31 @@ describe('serializerCompiler', () => {
     expect(result.json()).toEqual({ jobId: '60002023' });
   });
 
+  it('should handle a route without a schema', async () => {
+    const app = fastify();
+
+    app.setSerializerCompiler(serializerCompiler);
+    app.post(
+      '/',
+      {
+        schema: {
+          response: {
+            200: {},
+          },
+        },
+      },
+      async (_req, res) =>
+        res.send({
+          jobId: '60002023',
+        }),
+    );
+    await app.ready();
+
+    const result = await app.inject().post('/');
+
+    expect(result.json()).toEqual({ jobId: '60002023' });
+  });
+
   it('should fail an invalid response', async () => {
     const app = fastify();
 

src/serializerCompiler.ts

@@ -6,6 +6,7 @@ import type { FastifySerializerCompiler } from 'fastify/types/schema';
 import type { ZodType, ZodTypeAny } from 'zod';
 import { createSchema } from 'zod-openapi';
 
+import { isZodType } from './transformer';
 import { ResponseSerializationError } from './validationError';
 
 export interface SerializerOptions {
@@ -16,6 +17,10 @@ export interface SerializerOptions {
 export const createSerializerCompiler =
   (opts?: SerializerOptions): FastifySerializerCompiler<ZodType> =>
   ({ schema, method, url }) => {
+    if (!isZodType(schema)) {
+      return opts?.stringify ?? JSON.stringify;
+    }
+
     let stringify = opts?.stringify;
     if (!stringify) {
       const { schema: jsonSchema, components } = createSchema(schema, {