code: private void checkAndAddLengths(final int... requiredLengths) {
  		for( final int length : requiredLengths ) {
  			if( length < 0 ) {
  				throw new IllegalArgumentException(String.format("required length cannot be negative but was %d",
  					length));
  			}
  			this.requiredLengths.add(length);
  		}
  	}
docs: Adds each required length, ensuring it isn't negative.
  
  @param requiredLengths
  one or more required lengths
  @throws IllegalArgumentException
  if a supplied length is negative