Using if statement to deal cards

I am trying to deal an x amount of cards to a player depending on how many they already have in their hand (max of 5). But to insure that you don't get dealt the same card twice, or dealt a card that has already been played I've used an if Statement.

Card[] hand = new Card[5];
public void dealCard() {
  int cardCount = 0;
  Random ran = new Random();

  if (cardCount < 5) {
    int times = 5 - cardCount;
    for (int l = 0; l < times; l++) {
      int index = ran.nextInt(deck.length);
      if (deck[index] != null) {
        hand[cardCount] = deck[index];
        deck[index] = null;
        cardCount++;
      }
    }
  }
}

It seemed to work at first but every so often the last card, and its always the last card, is null. I was told that it would probably be better to use a while loop instead, but just for the purpose of learning what have I done wrong here.