call getter function return Unsupported item type: tvm.stackEntrySlice

Why does this simple getter function always return an Unsupported item type? I also tested common types like String, and Int but only on returning structs have error.

```
get fun query(index: Int): Order? {
      return self.orders.get(index);
}
```
the client app call using tonClient 

```typescript
query: () => {
    console.log(contract?.getQuery(BigInt(1)));            
}
```
