[http] Strange behaviour around sending reference types

I am trying to implement a command which has Type either `*big.Int` or `big.Cid`.

1. When using no `Type` and only `MakeEncoder` and send `big.NewInt(0)` I end up with the error `unexpected type float64 (expected interface {})`
2. When I try to wrap the result in something like this:
```go
type result struct {
myint *big.Int
cid *cid.Cid
}
```
and use `Type: &result{}`, I end up with result being nil when sending `result{myint: big.NewInt(0)}`