If no struct tags are provided, the struct decoder will only work if the lowercased struct field name matches the BSON key. This doesn't work for camel-cased fields.

For example, if the BSON key is "firstBatch", the struct decoder will not find it in the struct because it is looking for "firstbatch".

Filing this as a question ticket because I'm not sure what we want the behavior to be. At the very least, we should document this behavior and encourage users to always use struct tags.