code: @Override
  	public CounterOperation decrement(final String counterName, final long amount)
  	{
  		Preconditions.checkNotNull(counterName);
  		Preconditions.checkArgument(!StringUtils.isBlank(counterName));
  		Preconditions.checkArgument(amount > 0, "Decrement amounts must be positive!");
  
  		// Perform the Decrement
  		final long decrementAmount = amount * -1L;
  		return this.mutateCounterShard(counterName, decrementAmount, Optional.<Integer> absent(), UUID.randomUUID());
  	}
docs: /////////////////////////////