driver-core/src/main/com/mongodb/connection/ClusterDescription.java
@Deprecated
    public List<ServerDescription> getPrimaries() {
        return getServersByPredicate(new Predicate() {
            public boolean apply(final ServerDescription serverDescription) {
                return serverDescription.isPrimary();
            }
        });
    }
@Deprecated
    public List<ServerDescription> getPrimaries() {
        return getServersByPredicate(new Predicate() {
            public boolean apply(final ServerDescription serverDescription) {
                return serverDescription.isPrimary();
            }
        });
    }
While it may seem counter-intuitive that a MongoDB cluster can have more than one primary, it can in the case where the client's view
of the cluster is a set of mongos servers, any of which can serve as the primary.

@return a list of servers that can act as primaries
@deprecated Replace with a filter on ServerDescription in the caller