rsnext/errors/invalid-server-options.md
Todor Totev bad376127e
Detailed error and warnings upon next() call (#13539)
**First, apologies for a second PR on the same issue but I was working on this already so I thought I'd push it and let you decide which you want to merge.**

The PR is related to [13466](https://github.com/vercel/next.js/issues/13466).

Based on my research, the error happens if the options are empty, null, or undefined. That's why I have decided that the most proper check would be using the! post-fix expression operator may assert that its operand is non-null and non-undefined. ``if (options == null)``

(Optional)
I have also added a warning, which warns the user if the passed "dev" variable is not a boolean.

It's my first PR on the "packages" part of the repo so I'd be glad to receive all kinds of critics. If you want me to change or remove anything, I'm open to suggestions.

---

Fixes #13466
2020-06-03 03:19:29 +00:00

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Markdown

# It looks like the next instance is being instantiated incorrectly.
#### Why This Error Occurred
You have passed a null or undefined parameter to the next() call.
#### Possible Ways to Fix It
Make sure you are passing the variables properly:
```js
const app = next()
```
And make sure you're passing dev as shown in the examples below:
```js
const app = next({ dev: boolean })
```
### Useful Links
- [custom-server-express](https://github.com/vercel/next.js/blob/6ca00bfe312c8d3fc5c20d25a9cd8d2741a29332/examples/custom-server-express/server.js#L6)
- [custom-server](https://github.com/vercel/next.js/blob/6ca00bfe312c8d3fc5c20d25a9cd8d2741a29332/examples/custom-server/server.js#L6)
- [custom-server-typescript](https://github.com/vercel/next.js/blob/6ca00bfe312c8d3fc5c20d25a9cd8d2741a29332/examples/custom-server-typescript/server/index.ts#L7)