김명철

fix(query-core): Change to prevent `undefined` from overriding Mutation default side effects.

2

## Problem `undefined` means a variable that has not been assigned. Therefore, when the `onError` property in `useMutation` receives `undefined`, the side effects of the default options are retained and...

```ts type CamelCase = Lowercase extends `${infer A}_${infer B}${infer C}` ? Uppercase extends B ? `${A}_${CamelCase}` : `${A}${Uppercase}${CamelCase}` : Lowercase 1. Find the pattern using `Lowercase`. 2. If B is...