[Q] Is type assertion check needed for resolver params?

Type cast code: https://github.com/graphql-go/graphql/blob/master/examples/todo/main.go#L156

```go
idQuery, isOK := params.Args["id"].(string)
```
args for type: https://github.com/graphql-go/graphql/blob/master/examples/todo/main.go#L149
```go
Args: graphql.FieldConfigArgument{
"id": &graphql.ArgumentConfig{
Type: graphql.String,
},
},
```

Since the arguments validation is done in GraphQL schema layer.The `id` parameter must be a string type in resolver.
So I think it's unnecessary to check `isOk` variable. Am I correct?