code: public String set(final int i, final String value) {
  		final ConfigBlock block = this.blocks.get(i);
  		if (block instanceof ConfigItem) {
  			final ConfigItem item = (ConfigItem) block;
  			final String previousValue = item.getValue();
  			item.setValue(value);
  			return previousValue;
  		}
  		return null;
  	}
docs: Set a value for an item at a given index
  @param i the index
  @param value the new value
  @return the previous value
  @throws IndexOutOfBoundsException if the index is out of range (index < 0 || index >= size())