Decoder doesn't display a type mismatch

We had a situation like 
```go
type WLB struct {
	Accessmask          []string `json:"accesmask"`
	...
```

But sometimes in our dataset, this field was actually just a `string`. 
The error that the json.Decoder.decode() was `json: slice unexpected end of JSON input`.

Shouldn't the error be that the value doesn't have the expected type instead?