Ruby Koan for Dice Scoring (Greed) - Solution #2

It's interesting what some sleep and exercise can do.  The next day while approaching the "big hill" part of my run I came up with a new solution to the Greed Ruby Koan.  This solution is shorter and is more Rubyesque (I think). It also includes a reasonable amount of error checking (nil parameter and valid dice values).  Again, I'd love to hear from Ruby enthusiasts to comment on style and other approaches.

def score(dice)

  return 0 if dice == nil

  score  = 0
  counts = [0, 0, 0, 0, 0, 0]
  dice.each { |roll| counts[roll-1] += 1 if (1..6) === roll } # Count valid rolls

  (1..6).each { |i| score += (i == 1) ? 1000 : i * 100 if counts[i-1] >= 3 } # Score triples

  # Score the rest
  score += counts[0] % 3 * 100
  score += counts[4] % 3 * 50

  return score
end