# Function: checkFilter()

```ts
function checkFilter(
   filter, 
   at?, 
   options?, 
   depth?
): string | null;
```

Defined in: [packages/core/src/query/filter.ts:169](https://github.com/leifriksheim/minca/blob/main/core/src/query/filter.ts#L169)

Why a filter can't be used, or null. `include` lets it read `include:<name>`,
what a rule's query included.

## Parameters

| Parameter | Type | Default value |
| ------ | ------ | ------ |
| `filter` | `unknown` | `undefined` |
| `at?` | `string` | `'where'` |
| `options?` | `FilterOptions` | `{}` |
| `depth?` | `number` | `1` |

## Returns

`string` \| `null`