Swagger error: response check failed: void does not allow value

Question

I just follow the egghead Build Node.js API with the OpenAPI Spec tutorial (Swagger). I wrote a function to save data, as in the tutorial, but when I try to save data, I have

Build Node.js API with OpenAPI Spec (Swagger)

{ "message": "Response validation failed: void does not allow a value", "code": "INVALID_TYPE", "failedValidation": true, "path": [ "paths", "/", "post", "responses", "200" ], "originalResponse": "{}" } 

I'm new to this, so please can someone help me with this