It doesn't work when input argument is null

### What happened?

**The input schema**

```
extend type Query {
apiResponse(id: ID!,filter:MakerFilterInput): Any
}
```

** when run the query**

query httpresp {
apiResponse(id:"xxxx") // The arg "filter" is null, get the error: but if the filter is not null.it works well
}

**error**:

```

{
"errors": [
{
"message": "internal system error",
"path": [
"apiResponse"
]
}
],
"data": {
"apiResponse": null
}
}
```

### What did you expect?

### Minimal graphql.schema and models to reproduce

### versions
- `go run github.com/99designs/gqlgen version`? v0.17.14
- `go version`? 1.18

该 issue 涉及一个 GraphQL 查询：当省略 nullable 输入参数时（将其视为 null），查询会失败。查看输入处理的代码生成部分，可能位于 resolver 中，或位于为 'apiResponse' 字段生成的代码中。检查 resolver 签名和内部逻辑如何处理 null 参数。运行提供的最小 schema 和查询，以复现 'internal system error' 并跟踪堆栈。

由索引模型根据 Issue 内容生成。