crystal compiler can't deduce that all values of uint is handled

crystal_compiler_wat

  arg_size = args.size.to_u
  # wrong number of arguments
  if arg_size == 0 || arg_size > 2
    next "wat.  try #{Command.all["!feed"].description}"
  end

  ducky = Ducky.find_by(username: args.first.downcase)
  # cant find ducky to feed
  if ducky.nil?
    next "hmm.. #{args.first} should !start_record to recieve feed"
  end

  case arg_size
  when 1
    points = 10
    # give ducky the default amount of points
  when 2
    points = args.last.to_i { 0 }
    # try* to parse to int, if not default to 0
  end
  
  points.not_nil!
  # we have covered all possible values for u_int
  # (see line 17, 27-34)
  # not sure if this is the best way to handle...

  if points.zero