public ID getCoordinator(
      Collection<ID> rejections) {
    if (rejections == null) {
      return getCoordinator();
    }
    synchronized (membersLock) {
      for (ID addr : members) {
        if (addr.preferredForCoordinator() && !rejections.contains(addr)) {
          return addr;
        }
      }
      for (ID addr : members) {
        if (!rejections.contains(addr)) {
          return addr;
        }
      }
    }
    return null;
  }
Returns the coordinator of this view, rejecting any in the given collection of IDs
geode-membership/src/main/java/org/apache/geode/distributed/internal/membership/gms/GMSMembershipView.java