Random number generator giving inconsistent results

I am trying to work out how to add 6 randomly generated numbers to a HashSet. I am getting results but they are inconsistent. Sometimes it prints 6 numbers to the console and other times it prints 5 numbers to the console.

I'm new to this stuff only this morning so I apologize if it is blatantly obvious and thank you for your help.

 HashSet<Integer> GeneratedLotteryNumbers = new HashSet<Integer>();
Random r = new Random();

for(int i=0; i<6; i++){
  GeneratedLotteryNumbers.add(r.nextInt(49));
}

System.out.println(GeneratedLotteryNumbers);