NEW DESCRIPTION
mgo supports a non-default option to fallback to using json tags for structs when bson tags aren't present, so an option should be added to StructCodec to do the same.
PREVIOUS DESCRIPTION
Basically if you have a struct that has something like:
```
WsId string `json:"ws_id"`
```
Running find() on a collection will not return the ws_id field for the document, but if you define the struct as:
```
Ws_Id string `json:"ws_id"`
```
It will work.
Read this - https://github.com/golang/go/issues/40351