code: public void setLabel(String labelValue)
  			throws IllegalArgumentException {
  		if ((labelValue == null) || (labelValue.length() == 0))
  			throw new IllegalArgumentException("Part's label can't be null or empty!");
  		m_label = labelValue;
  		m_music.setPartLabel(m_label);
  	}
docs: Sets the label which first char identifies this part.
  
  @param labelValue
  The label that identifies this part.
  @throws IllegalArgumentException if label is 0-length