Suppress test on fields and excludeFields selectors

The following projection is allowed by MongoDB, but not by the current implementation of this package.
     { "_id": 0, "foo": 1}

In other words, leave MongoDB server to handle the error management.

You cannot combine inclusion and exclusion semantics in a single projection with the exception of the _id field.
http://docs.mongodb.org/manual/tutorial/project-fields-from-query-results/