Well,
I started using another method of the indicators class - namely:
long prevBarTime = history.getBar(instrument, Period.THIRTY_MINS, OfferSide.ASK, 1).getTime();
double[][] maxArray = indicators.minMax(instrument, Period.ONE_HOUR, OfferSide.ASK, AppliedPrice.HIGH, 55, Filter.WEEKENDS, prevBarTime, prevBarTime);
I guess, because I tested it on a monday, the weekend was also considered by the minmax algorithm, which didn't show on the chart. So I am using the above method in which I started to use the Filter.WEEKENDS field as well. The method itself is a little tricke because of the bartimes you have to take in consideration as well - and it gives you for no obvious reason a two-dimensional array in return. But who cares, it seems to work.
Thank you very much for your help, I really appreciated it.