public NullChallenge(
IRankIdentifier rankIdentifier = null,
IClashResolver clashResolver = null)
: base(rankIdentifier, clashResolver)
{
}
protected Challenge(IRankIdentifier rankIdentifier, IClashResolver clashResolver)
{
this.clashResolver = clashResolver;
this.rankIdentifier = rankIdentifier;
this.nextChallenge = NoChallenge;
}