As part of mgo->go driver migration, I found weird failures in evg: 
https://evergreen.mongodb.com/version/5c75aecd2fbabe2eb0b55062 . 
more specifically the error: 

Err: cannot transform type bson.D to a BSON Document: WriteArray can only write a Array while positioned on a Element or Value but is positioned on a TopLevel

The code caused this error: 
session.Database("admin").RunCommand(context.Background(), bson.D{{"buildInfo", int32(1)}}).Decode(&result)

(https://github.com/10gen/mms-backup/pull/317/commits/7b5323541e89a0fb77609ecdea9c99469f31e3af)

By changing bson.D{{"buildInfo", int32(1)}} to bson.M

the error went away. 

Can you please take a look? thanks!

Note: no mgo imported nor deps installed