code: @Deprecated
      public List<ServerDescription> getPrimaries() {
          return getServersByPredicate(new Predicate() {
              public boolean apply(final ServerDescription serverDescription) {
                  return serverDescription.isPrimary();
              }
          });
      }
docs: 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