code: public boolean hasNotes() {
          for (Object m_staffElement : m_staffElements) {
              JScoreElement element = (JScoreElement) m_staffElement;
              if ((element instanceof JNoteElementAbstract)
                      || (element instanceof JGroupOfNotes))
                  return true;
          }
  		return false;
  	}
docs: Returns true if this staff line has note(s).
  Returns false if it only contains clef, key, time sig., tempo, barlines...