code: private ValueHolder getHolderByIntervalName(String aIntervalName){
  		ValueHolder h = values.get(aIntervalName);
  		if (h == null)
  			throw new UnknownIntervalException(aIntervalName);
  		return h;
  	}
docs: This method returns the ValueHolder that is stored for the given Interval name.
  
  @param aIntervalName the name of the interval
  @return the stored ValueHolder
  @throws UnknownIntervalException if there is no ValueHolder stored for an Interval with the given name